Aquarium problems

Are algae a problem or are your aquarium plants not growing well? Is the water cloudy or are your fish ill? Don’t your water parameters correspond to your expectations?

Our team of experts has thoroughly analysed such problems and offers you solutions to your problems in the aquatic field, which really work.

water cloudiness & water discolouration

There are two main types of cloudiness: greenish cloudiness and whitish cloudiness. In addition there are also colour casts, which can make the water look brownish or yellowish.

Then we have the following advice for you:

Whitish water cloudiness

In most cases this is caused by bacteria/microorganisms and it disappears on its own after 1 – 2 days. If not, using a UVC water clarifier (JBL AquaCristal UVC) can help. The power (wattage) of the UVC water clarifier depends on the water volume of the aquarium. Operating principle: The water flows relatively slowly inside the UVC water clarifier, passing the germ-killing UV radiation. This radiation kills off the germs and bacteria, as well as the floating algae. Their whitish cloudiness will completely disappear within 1 – 3 days!

Greenish water cloudiness

This is caused by floating algae, which make the water look greenish. This generally occurs more in ponds than in aquariums. For the aquarium an anti-algae agent (JBL Algol) or the use of UVC water clarifiers (JBL AquaCristal UV-C) are useful. The power (wattage) of the UVC water clarifier depends on the water volume of the aquarium. Operating principle: The water inside the UVC water clarifier flows relatively slowly along the germ-killing UV radiation. This kills off the floating algae.

Yellowish discolouration

A discolouration is mostly caused by medication (e.g. blue colouring) or phenolic substances, which arise during different degradation pathways (yellowish colouring). The use of activated carbon (JBL CarboMec) in the filter system provides the fastest help. Activated carbon binds dye and thus creates clear water without a colour cast.

Brownish discolouring

A brownish discolouration is often caused by humic acids which, for example, are dissolved out of peat or wood. In case the use of activated carbon (JBL CarboMec) does NOT help, you either have to live with the brownish tint (which has no harmful effects!), the piece of wood has to be removed, or you try another piece of wood. Hard woods (opuwa, mopani) often cause lower or no discolouring in comparison to softer woods, such as mangroves or bog wood.

Problems with aquarium plants

If you have problems with aquarium plants it is better to proceed systematically. Plants need light, carbon dioxide (CO2), minerals/trace elements, such as iron (Fe), as well as nitrogen in the form of ammonium or nitrate and moreover phosphate for their growth.

If we go through these essential components chronologically, the problems with plant growth will surely be solved. As every aquarist knows, there is a biological law pertaining to plant growth, which was laid down by Mr. Justus von Liebig as early as 1828. It states that the growth of plants is limited by the relatively scarcest resource (nutrients, water, light etc.). This resource is known as the minimum factor. If such a deficiency factor occurs, the adding of a resource which is already available in the required extent has no influence on the growth. This law of the minimum is among other things an important basis for the fertilization (Example: The plant has a lack of CO2. Because of this lack it can’t grow sufficiently even if fertilizer and light are then supplied in large quantities.).

With this online calculator you can calculate the ideal fertiliser supply for your aquarium: ProScape dosage calculator

And please don’t forget to check whether herbivorous fish or invertebrates are inside the aquarium. The popular bushy nose plecos (Ancistrus) are not only algae eaters but also herbivores!


Plants contain leaf green which enables them to use light energy for food production. The leaf green (chlorophyll) uses the full visible spectrum, as we know it from the rainbow. UV radiation and infrared light are not used for that process. With this knowledge it is understandable that plants can certainly also use “incandescent light”. But they can produce more energy with the light of all the colours of the spectrum compared to the typical light of the incandescent lamp. Fluorescent tubes for residential premises, which are often significantly cheaper than typical aquarium tubes, also deliver appropriate light. But also here the light spectrum is designed to make a room bright, not for the leaf green of the plants. JBL has fluorescent tubes with a full spectrum in its product range (JBL SOLAR tubes), which provide the full spectrum equivalent to sunlight. They are recognized by specialists as being the best lighting for aquariums and have been chosen by research facilities, such as the IFM Geomar in Kiel, to be used for sun light simulation.

In addition to the light quality the light quantity is also of importance. Light green and reddish plants need more light than dark green plants and this rule of thumb makes the choice of plants for one’s own aquarium somewhat easier. In the DATZ lexicon „Aquarium Plants” by Christel Kasselmann you will find a table showing which plants need which light requirements.

Daylight is not desirable for aquariums, even though it is supposed to provide the perfect light. This is due to the fact that an excessive amount of the aquarium nutrients are present, and this, together with the huge light quantity in daylight, leads to algae growth. Daylight has a light quantity of about 100,000 lux, whereas a T8 fluorescent tube emits only 700 lux. A good reflector doubles the light efficiency and T5 tubes produce about twice the light quantity as T8 tubes!

But still we should bear in mind that most aquariums are insufficiently illuminated and we should, whenever possible, chose a canopy with the maximum number of tubes. From a physical point of view it is also interesting that although the light quantity of 2 tubes with 15 watts each results mathematically in 30 watts, the same light quantity does not reach the bottom of the aquarium as with a 30 watts tube.


  • Use only full-spectrum tubes such as the JBL SOLAR Tropic or Natur. Whenever possible, it’s better to use 2 tubes than one. Tube combinations: “plant tubes” like the JBL SOLAR Tropic go over the plants (usually at the back). Bright bulbs (e.g. SOLAR Natur) go at the front above the fish. Colourful bulbs, such as the JBL SOLAR Color, show up the fish’s colour better but, when there are high levels of nutrients (phosphates and nitrates), also stimulate algae growth.
  • T5 tubes have a higher light efficiency than T8 tubes. You should therefore give the T5 bulbs preference over the T8 bulbs. The tubes cannot be simply swapped over. T5 and T8 tubes have completely different electronic backup and require each their own ballasts and sockets!!!

carbon dioxide (CO2)

CO2 is THE staple food for plants and often the limiting factor for plant growth in the aquarium. CO2 occurs naturally in the aquarium, caused by respiration processes (inhaling of oxygen and exhaling of CO2), amongst other things. However the CO2 amount is not sufficient for a luxuriant plant growth and needs to be supplemented by a CO2 fertiliser system (e.g. JBL ProFlora bio80, JBL ProFlora u401 oder JBL ProFlora m601). Many plant species, especially very reddish plants, require a high CO2 concentration to grow in the water. Without CO2 fertilization they can’t be cared for sufficiently.


Reduce the movement of the water surface in the aquarium so as not to expel too much CO2. Air stones really are CO2 killers. Connect a CO2 system, such as the inexpensive JBL ProFlora bio80, even to the smallest aquariums, and you will notice how much better your plants will grow! For larger aquariums it’s worth investing in CO2 systems with refillable CO2 pressure cylinders such as JBL ProFlora m601. Those without a filling station nearby can also choose a disposable system such as JBL ProFlora u401.

Mineral fertilizers and trace element fertilizers

For most people plant fertilization means the adding of a liquid fertilizer as with potted plants on the windowsill.

The fertilization of aquarium plants however differs in 3 crucial aspects:

  • Nitrogen (N) reaches the water through fish excrement, amongst other things, and does not need to be added with the fertilizer. Additional nitrogen fertilizing is only useful in pure plant or invertebrate aquariums.
  • Land plants absorb the CO2 from the air where it is available in unlimited amounts. For water plants we need to use a CO2 fertiliser system.
  • Land plants need phosphorus in fertilizers. For water plant phosphorus is present in excess in the water and therefore should only be added to pure plant and invertebrate aquariums (JBL NanoFerropol24 Moos). Water plants absorb nutrients through their leaves and, depending on the species, also through their roots. Thus a soil fertilizer (JBL AquaBasis plus, JBL The 7 Balls, JBL Florapol) is very helpful for aquarium plants. A substrate heater, such as JBL ProTemp b, helps by circulating the heat at the bottom and “flushing” the nutrients evenly around the plant roots.

However even the nutrients in the soil fertilizer are used up after several weeks and – just like a rechargeable battery – need to be replenished. For this purpose the liquid basic fertilizer JBL Ferropol is available, containing almost all essential trace elements for perfect plant growth. Unfortunately some essential trace elements are extremely susceptible to a reaction with oxygen (such as the rusting of iron) and therefore can’t be fertilized “on stock” every two weeks. That’s why JBL has designed a daily fertilizer (JBL Ferropol 24) which adds trace elements daily.

What to do:

When setting up a new aquarium use a long-term nutrient substrate, such as JBL AquaBasis plus, and a plant-friendly substrate, such as JBL Manado, for thriving plant growth. With JBL Ferropol the basic fertilizer should be added in two week intervals, supplemented by the daily fertilizer JBL Ferropol 24. With the help of the JBL Iron Test Fe the fertilizer content in the water can be checked to perfection.


Plant growth is definitively not achieved by magic! If you check and modify the above mentioned point, you will be rewarded by thriving plant growth.

Trouble shooting

Brownish discolouration is often caused by humic acids which are often dissolved out of peat or wood. Should activated carbon (JBL CarboMec) NOT help, you will either have to live with the brownish tint (which has no harmful effects!), remove the wood or try another piece of wood.

  • Iron deficiency (chlorosis)

    Iron deficiency leads to light green, yellowish, glassy or pale leaves. The set point value for the iron content (Test Set Fe) amounts to 0.05 – 0.2 mg/l. JBL Ferropol is most suitable to raise the iron content. If you already use a fertilizer, but the iron test doesn’t indicate any sufficient values, this may be for one of the following reasons: Your fertilizer contains iron, but in a form (Fe2+), which is oxydised in water by the oxygen (it reacts with the oxygen) and thus has no benefit for plants; your fertilizer doesn’t contain any iron.

  • Manganese deficiency

    An insufficient supply of manganese caused by an inappropriate fertilizer leads to yellowish leaves, on which, unlike with chlorosis, only the leaf veins stay green and come to the fore (Christmas tree disease). This can be remedied by JBL Ferropol, which contains many other trace elements, such as manganese, in addition to iron.

  • Lack of light

    In case of insufficient light many plants develop diseased growth forms. They etiolate (long stems with fewer leaves per unit length of stem), lose the lower leaves or they deteriorate. Only with the right and sufficient light (JBL SOLAR full spectrum tubes) will they develop their natural growth form.

  • Lack of CO2

    When there is a lack of CO2 the plants (and also the algae) take the bound CO2 from the carbonate hardness, which is then destroyed, and drops. This process is known as biogenic decalcification and can be seen by the decrease of the KH and the whitish precipitate on the plant leaves (often on their edges).

  • Crypt melt

    Is often caused by the changing of care conditions and by transplantation. This can only be remedied by constant care conditions and the reduction of the nitrate level to below 50 mg/l.

  • Nitrate quantity (NO3 content)

    Nitrate quantities over 50 mg/l lead in many plants to stunted growth although nitrate in low concentrations acts as a supplier of nutrients. It can also lead to crypt melt. Remedy: partial water change and JBL BioNitrat EX. Good nitrate absorbers are e.g. Cabomba, Hygrophila and species of Limnophila.

  • Lack of trace elements

    Caution! Activated carbon does not only remove residues of medications and water discolorations but also minerals, trace elements and vitamins. Only add activated carbon to the filter in special cases!

  • Holes in the leaves, grid-like leaves

    Mainly caused by grazing. Check if there are any plant eaters in the stock of fish and invertebrates.

  • Extreme and fluctuating water values

    Extreme temperatures (< 18 °C or > 29 °C) as well as extreme pH levels (< 6.5 or > 8.0) or degrees of hardness (KH < 4° dKH or > 10 ° dKH) affect the plant growth. For remedy and correction of the water values see the JBL Online Lab.

  • Use of anti-algae agents

    “Stringent” anti-algae agents affect the plant growth significantly and may lead to death of the plants, because algae are closely related to the algae.

    Remedy: In case of problems with algae change to JBL Algol.

  • Plants get mushy and decay after some time

    Some popular aquarium plants are not actually underwater plants, but marsh plants which can survive for a time under water – but not for too long! Many water plants, such as Amazon sword plants, are cultivated emersed (out of water) and, when switched over to submersed growth (under water), immediately lose their over water leaves. All you can do is wait, or buy strictly underwater plants.

  • Rotting leaves and no leaves in the lower area

    Check the space and insertion requirements! Stem plants, such as Vallisnerias or Cabomba are often wrongly inserted. Remove the lead before you insert them separately at an even distance to each other. Don’t forget to remove potted plants from their pots.

Aquarium water tests

Did you test your aquarium water and get bad results? Aquarium water tests are the key to functioning aquariums! Here is a free, on-the-spot analysis of your water test results. Water Analysis Online Laboratory

Or would you like detailed information about the individual water parameters? You will find it here.

Water hardness

The water hardness is divided into general hardness (GH) and carbonate hardness (KH). The correct scientific definition of both parameters isn’t really a big help for the beginner: The GH is the overall concentration of the alkaline earth metals (e.g. calcium ions and magnesium ions) in the water. The KH is defined as the amount of all carbonates and hydrogen carbonates.

Are you with me? To put it more simply, the general hardness is a measurement of a specific content of minerals in the water and the carbonate hardness indicates the pH stability of the water. For most aquarists and pond owners the KH is the more important value because the KH stabilizes the pH level (acidity of the water). A too low KH (below 4 °dKH) causes strong fluctuations in the pH level. It then can either slip down (sudden drop in acidity) or it moves upwards. Both can be toxic for the organisms and therefore it is essential to check (JBL KH Test Set) and stabilize (JBL AquaDur) the KH level.

In some tropical waters, including Lake Malawi and Lake Tanganyika, the conditions are the other way round: The KH is higher than the GH. What is the reason for that? Here soda sources are the reason for a high share of sodium bicarbonates, which may increase the KH level, whereas sodium simply doesn’t contribute to the total hardness. To reproduce this situation in the aquarium, JBL has designed AquaDur Malawi-Tanganjika. With this special salt the natural water composition can be reproduced.

Increasing the water hardness: Why is it necessary? Some animals don’t feel comfortable in very soft water (low water hardness). An increase could be appropriate to the species, if you only have tap water with low hardness available. If the carbon hardness is below 4, you have a very soft water which runs the risk of pH fluctuations. In this case raising the KH is strongly advised.

Increasing the general hardness (GH): Sodium chloride doesn’t help! Sodium chloride only contains sodium (Na) and chloride (Cl). Neither of these substances has an influence on the GH. It is normally never necessary to raise the GH and not the KH. To increase the GH and the KH to the same extent, a special salt, such as JBL AquaDur, it suitable.

Increasing the carbonate hardness (KH): Again in this case sodium chloride doesn’t help. An addition of sodium bicarbonate raises the KH level but not the GH level. With JBL AquaDur both, the GH and the KH, can be increased to the same extend. JBL AquaDur Malawi/Tanganjika increases the KH level more than the GH level. The biological processes in aquariums can lead to the entire carbonate hardness being used up! The reason is that water plants (and therefore also algae!) elute the essential CO2 from the KH, if there is not enough free CO2 in the water. This leads to a dramatic drop in the KH level. This process is known as biogenic decalcification. Calcareous materials (coral sand, clamshells, marble, coral skeletons etc.) only increase the hardness if the pH level of the water is below 7. Only then is there sufficient acid to dissolve materials in water. In alkaline pH levels (above 7.0) nothing happens.

Decreasing the water hardness: Why is this necessary? Many aquarium inhabitants originate from soft water areas such as the Amazon or the Rio Negro. To meet their specific needs a reduction of hardness is recommended. But instead of fiddling around with the water parameters every few days a regular partial water change is a much better idea! Again many water plants have their origin in soft rather than hard waters. Garden ponds tend to have too soft water because the rain water reduces the mineral content. To reduce the hardness: For regions with hard tap water a reduction of the water hardness can help accommodate the specific needs of invertebrates, fish and plants. Water softening is quite simple with the help of a reverse osmosis unit. The unit is connected to the water tap to filter 95 % of all hardness formers (and also pollutants) out of the water. The addition of pH decreasing aids (e.g. JBL pH-Minus) result in a reduction of KH but must implemented carefully. The addition of a pH reducer needs to be carried out in very small steps and permanently monitored by means of KH and pH tests. Do not perform at all with a KH of below 4. A water change is only useful, when the tap water has a lower hardness than the aquarium water.

Nitrogen compounds (ammonium, nitrite, nitrate)

In the aquarium nitrogen compounds are produced which can create problems in certain quantities or even be lethal for the animals. Therefore ammonium (NH4)/ammonia (NH3), nitrite (NO2) and nitrate (NO3) must be measured regularly. For this purpose easy to use and highly accurate water tests (JBL test sets) or even complete test cases (JBL TestLab) are available. People often talk of the so called nitrogen cycle in which the substances mentioned break down into the next one respectively. These degradation processes take mainly place in the filter system (and the substrate). There protein is broken down to ammonium by bacteria (or with a pH level over 6.0 also to ammonia). This is then also bacterial transformed into toxic nitrite and this again into the non-toxic but algae-promoting nitrate.

New aquariums do not yet have sufficient bacteria to start the break down processes. That’s why they need the support of bacteria starters (JBL Denitrol, JBL Filterstart, JBL FilterBoost). Merely waiting before adding the animals is often not enough, because the existing bacteria reproduce only with a sufficient supply of nutrients.

Ammonium (NH4)/ammonia (NH3): This is the first link of the chain for the nitrogen removal. Ammonium is excreted through the gills of the fish or created during the bacterial conversion of proteins. Ammonium (NH4) is non-toxic, but an increased concentration in the water hinders the fish from “breathing” the ammonium out of its gills. At a pH level of over 6.0, part of the non-toxic ammonium converts into toxic ammonia (see table XX). Normally the ammonium produced is oxidized to nitrate via nitrite by means of bacteria. If ammonium can be detected in the water this is a sign of a disturbance of the bacterial degradation processes. The bacteria required for this are either not sufficiently available (new aquarium) or affected (medications, addition of salt, UVC water clarifier).

Reduction of the ammonium/ammonia content: In case of an ammonia poisoning (fish dart backwards and forwards, gasp at the water surface) an immediate lowering of the pH level is a possible first aid measure, as this converts the toxic ammonia back into non-toxic ammonium on the spot. Further steps are then necessary to deal with the problem long term. These steps include a water change and the addition of bacterial starters (JBL Denitrol, JBL Filterstart, JBL FilterBoost). Additionally JBL has a filter material in the product range, which directly absorbs the ammonium from the water (JBL AmmoEX). Increase of the ammonium/ammonia content: This is never necessary and therefore not useful.

Nitrite (NO2): Nitrite is highly toxic, just like ammonia. It inhibits the oxygen transport in the blood (also in humans) and leads to inner suffocation. It should never show up on the JBL nitrite test because bacteria normally break it down into the non-toxic nitrate as soon as it develops. The detection of nitrite is either a sign of a disturbed bacterial activity or it indicates that an excessive occurrence of pollutants is overtaxing the bacteria.

This is an indication that the care measures have to be checked: Is it a result of overfeeding? Have there been too few water changes? Has an antibacterial remedy been added? Has salt been added (salt kills bacteria)? In exceptional cases an increased nitrite level can occur in newly set up aquariums because the bacteria are not fully developed yet. A good bacteria starter helps here (JBL Denitrol, JBL FilterStart) and a gradual stocking of fish. Never add all new fish in one go. Put them in the aquarium at intervals. That way the bacteria can adjust to the increasing amount of pollutants. With the use of JBL BioNitrat EX nitrate gets broken down via nitrite. Using too much JBL BioNitrat EX in one go could lead to a visible, but short-term rise in the nitrite level.

Reducing the nitrite content: Immediate water change (50 %), less feeding, regular partial water change (30 % every 14 days), regular siphoning of the substrate by means of a gravel cleaner (JBL AquaEX, JBL Aqua In-Out), adding of bacteria (JBL Denitrol, JBL FilterStart). Increasing the nitrite content: This is never necessary and therefore useless.

Nitrate (NO3): Nitrate develops during the nitrogen degradation by Nitrobacter bacteria under aerobic (oxygen-rich) conditions from nitrate and gets broken down to nitrogen gas (N2), carbon dioxide (CO2) and water (H2O) under anaerobic (oxygen-free) conditions. Although nitrate itself is (unlike nitrite) non-toxic, high nitrate levels can stunt the growth of fish (especially in juveniles) and can also inhibit the growth of many plant species. The main problem with nitrate is that it encourages algae and this is why the nitrate levels should never exceed the recommended 50mg/l.

Reduction of nitrate levels: A regular water change precludes high nitrate levels, assuming that it is not too strongly present in the tap water used. It is therefore vital to check the tap water parameters. With the help of a reverse osmosis unit (JBL Osmose 120) up to 50 % of the nitrate can be removed from the tap water. Through the use of JBL Nitrat EX both tap water and aquarium water can be freed of nitrate. JBL Nitrat EX contains synthetic resins, which withdraw nitrate from the flowing water. Once the exchange capacity has been exhausted, it can be simply and quickly regenerated with sodium chloride. JBL BioNitrat EX has been designed for long-term use in the filter. This specific filter material contains a substrate which is colonized by nitrate-eliminating bacteria. It is enclosed by special mesh bags, which reduce the water flow to lower the oxygen content inside the bags. Then the bacteria living on the carbon-containing substrate split the nitrate to reach the oxygen within. Thus nitrate is removed from the water naturally, without side effects and long term (about 6 months).

Anyone wishing not only to remove nitrate, but also nitrite and phosphate at the same time, will find the right filter material in JBL ClearMec plus. Increasing nitrate levels: In most aquariums an increase of the nitrate level is not useful. There is only one case where nitrogen should be added: In pure plant aquariums and shrimp aquariums, where almost nothing is fed, a nitrogen deficiency for the plants can result. For such cases JBL has a dedicated fertilizer in the product range (JBL NanoFerropol24 Moos), which contains not only nitrogen but also phosphorus and potassium.


Phosphate (PO4): Phosphates and nitrates (NO3) are primarily plant fertilizers but have also a growth promoting effect on algae. This often happens in aquariums with normal to high fish stock where they are present in such high concentrations as to be in excess. Only in aquariums without or with low fish stock (e.g. aquascaping)are nitrate and phosphate present in insufficient concentrations and need to be added (JBL ProScape NPK fertiliser). Almost every fish food contains phosphate, which is important for the bone structure of the fish. However many fish foods contain too much phosphate because they use cheap fish meal for their production. JBL does not use fish meal, but instead processes high quality proteins made of fish fillet, to which a well-balanced mineral mix (ash content) is added afterwards for healthy fish growth. It is essential for the aquarist to choose the right food quantity to prevent overfeeding and the exposure to excess phosphate that may arise from this.

Be careful with frozen food! Most frozen foods are real phosphate bombs!!! When they die plant parts and algae release the phosphate amounts which were bound during their growth, and therefore need to be removed. Water plant fertilizers, filter materials and additives in the water, such as peat extracts, should never contain phosphate. Please check the products you are using. JBL products are guaranteed phosphate-free. A regular water change is surely one of the best measures against high phosphate levels, assuming that the tap water doesn’t contain any phosphate.

Please check your tap water before using it. Phosphates react quite quickly with minerals in the water and precipitates (sedimentation). It is therefore useful to use a gravel cleaner during a partial water change. Clean the filter too, as filter sludge contains large amounts of phosphate.

Reducing the phosphate level: In addition to the measures mentioned above, phosphate can easily, quickly and reliably be removed with the special filter material JBL PhosEX ultra. If you wish not only to remove phosphate, but also nitrite and nitrate, we recommend the dedicated filter media JBL ClearMec plus.

Increasing the phosphate levels: In most aquariums and in all ponds an increase of the phosphate level is not useful. There is only one case where phosphate needs to be added: In pure plant aquariums and shrimp aquariums where almost nothing is fed, a phosphate deficiency for the plants can result. For these cases JBL has dedicated fertilizers in its product range (JBL ProScape NPK Macroelements, JBL ProScape P Macroelements, JBL NanoFerropol 24 Moos).


The term salinity is relevant for both freshwater and saltwater. In saltwater the salinity can easily be measured with a hydrometer or a refractometer. Measurement by means of a conductivity meter is not reliable because the composition of the salt has an influence on the conductivity.

The salinity of the oceans is quite varied (it is higher, for example, in the Red Sea than in the Pacific) and essential for the keeping of the animals. In freshwater salt is often added for therapeutic reasons to be effective against bacteria and parasites. Here the salinity is adjusted with the dosage. By the way, the adding of salt to freshwater should be discontinued as quickly as possible. Neither the beneficial bacteria nor the water plants tolerate additions of salt.

Many aquarists measure the conductivity of their water by means of a conductivity meter (display in µS/cm or mS/cm). This way they can check if the conductance has changed when compared to the original water. If, for example, the tap water has a conductivity of 500 µS/cm and the aquarium water a higher conductivity of e.g. 900 µS/cm, this higher measured value indicates a direct addition of salt or an accumulation of pollutants. So the conductivity can be an indicator for water quality and the necessity for a change of water. Fans of discus fish, for example, like to keep their fish in soft water, which is water with very low conductivity, and add an osmotic salt (JBL AquaDur) to the osmosis water they use until they have reached the optimal conductance of e.g. 50 µS/cm.

Increasing the salinity: Addition of sea salt (in the saltwater), JBL EktolCristal or JBL AquaDur (in the freshwater).

Reducing the salinity: By means of tap or osmosis water in the saltwater. By means of osmosis water in the freshwater.


Oxygen is the elixir of life of most living beings in the water and therefore essential. The warmer the water, the less oxygen can be dissolved in the water. That’s why an additional aeration of the water is advisable and necessary. With too low oxygen contents the bacterial degradation capacity for pollutants drops, and below 2 mg/l fish begin to suffer from oxygen deficiency.

An important fact is that plants, exposed to light, produce oxygen but that they also consume oxygen in darkness. This is why it can be advisable during times of vigorous plant and algae growth to aerate the water. It is not true that low oxygen contents are a direct result of high carbon dioxide contents. Both gases can reach their saturation limit concurrently. But it is also often the case that a lot of carbon dioxide (CO2) gets expelled during an oxygen supply caused by surface movement (current, air stones, water jet pipes etc.). When the plants get supplied with carbon dioxide through a CO2 fertilization system, the CO2 content in the water rises simultaneously with the oxygen content because the plants produce oxygen during the assimilation.

Increase of oxygen content: The oxygen content in the water is ensured by a normal surface movement of the water. Aquariums which are of above average height often have a too small surface in relation to the water volume. This can make additional aeration necessary, or stronger water surface movements by means of water jet pipes or the like. Oygen tablets (e.g. JBL OxyTabs) are unsuitable for a long-term oxygen supply. In unplanted aquariums an additional oxygen supply with air stone can as well be useful. If aquariums should show a good plant growth, an aeration through air stones or strong water surface movements is not useful because the essential carbon dioxide (CO2) for the plant growth gets expelled.

Calcium and magnesium (only in saltwater)

Calcium (Ca) / Magnesium (Mg) Calcium is part of the general hardness (GH) and can be tested both in saltwater and in freshwater. Because of the very different quantities in fresh and saltwater this requires different tests. In marine aquariums the magnesium and calcium contents are of major importance for the care of invertebrates and red coralline algae. In freshwater the magnesium content is the decisive factor for successful plant care.

Increase of calcium: In saltwater there are different ways to raise the calcium content in the water:

1) JBL CalciuMarin: This product is ideally suited to increase the content of calcium easily, safely and without great technical effort and costs. One pack of JBL CalciuMarin contains 2 bags whose content has to be put into the aquarium in two places as far apart from each other as possible and at different times, as written in the instructions. A reaction will then occur between the two components inside the aquarium water. Calcium chloride and strontium chloride (bag 1) react with sodium hydrogen carbonate (bag 2) to create calcium bicarbonate, strontium bicarbonate and harmless sodium chloride. This process has come to be known under the name “Balling Method” in the marine fish keeping.

2) Chalk reactor: A chalk reactor is a container with calcareous material (calcium carbonate, coral sand, marble chips etc.) in its interior. The saltwater passing through gets enriched with carbon dioxide (CO2) whereby the pH level drops and the calcareous material dissolves slowly in the water. As a result hydrogen carbonates (KH) and calcium (Ca) dissolve in the water and get added drop by drop to the aquarium water. Chalk reactors are always used in combination with CO2 systems. JBL provides all the necessary components for this: compressed gas cylinders with 500 g and 2 kg contents, pressure reducer, solenoid valve and pH control unit.

3) Lime water: Lime water is defined as a saturated solution of calcium hydroxide (CaOH) which gets added drop by drop to the aquarium water. Through its hydroxide part (-OH) it raises the pH level of the saltwater and its calcium content. It doesn’t contain any carbonate hardness elements (HCO3), although it seems to have a KH of approx. 12 – 15. This illusion is caused by the hydroxide ions (OH-).

The trend in marine aquariums is no longer towards lime water but to chalk reactors and professional compounds, such as JBL CalciuMarin.

Magnesium (Mg): Magnesium is part of the general hardness (GH) of the water and can be tested in both saltwater and in freshwater. Because of the very different quantities in fresh and saltwater this requires different tests. In marine aquariums the magnesium content is of major importance for the care of invertebrates and especially for the beautiful growth of coralline algae. In freshwater the magnesium content is the decisive factor for successful plant care. Too high magnesium levels are not useful since the water has only limited absorption capacity for minerals and salts. If this capacity is occupied by too high magnesium levels, other essential minerals can no longer dissolve in sufficient quantities or they precipitate. Increasing the magnesium level: By adding JBL MagnesiuMarin (liquid preparation) to saltwater or adding JBL ProScape Mg Macroelements to freshwater, magnesium can be set easily, quickly and reliably to any desired level.

pH level

The pH level indicates the acidity and the alkalinity of the water. The more acid the water is (the more sour it is), the lower is the pH level. The less acid and more bases the water contains (the more alkaline), the higher the pH level. If the recommended pH level is too low, the aquarium inhabitants will no longer enjoy optimal living conditions. The bacterial filter activities will also drop sharply, and with values below 6 they will come to a standstill. That’s why the pH level should be increased to the specified value. The pH is a logarithmic value. This means that a reduction from pH 8 to pH 7 describes a tenfold increase and from 8 to 6 a hundredfold increase of the acidity.

Increase of pH level: Please check first, if the carbonate hardness (KH) corresponds with the recommended value. Before manipulating (raising or reducing) the pH level the KH MUST!!! be brought down to the recommended value (see chapter about KH). In most cases the pH regulates itself to the desired level. If however the pH level needs to be raised, this can be done by the addition of JBL pH-Plus (liquid pH increaser).

Reduction of pH level: Please check first, if the carbonate hardness (KH) corresponds with the recommended value. Before manipulating (raising or reducing) the pH level the KH MUST!!! be brought down to the recommended value (see chapter about KH).

In most cases the pH regulates itself to the desired level. If, however, the pH level needs to be reduced, there are three possibilities:

1) Through the addition of JBL pH-Minus (pH lowering liquid) the pH level can be reduced gradually. However the carbonate hardness will also drop simultaneously.

2) A dosed addition of CO2 (carbon dioxide) will not only fertilize the plants but will also lower the pH level. One part of the CO2 reacts with water to carbon acid (H2CO3), which reduces the pH level as do all other acids. For aquariums from 30 to 160 litres we recommend the JBL ProFlora Bio-CO2 fertilizer system; for aquariums from 60 to 1000 litres the JBL ProFlora systems u or m.

3) JBL TorMec (activated peat pellets) as a part of the filter material can slightly reduce the pH level. The activated pellets contain about 25 % humic acids which act as a pH reducer. In addition a slight softening occurs.

Diseases of aquarium fish

Are your aquarium fish ill? Do your aquarium fish show symptoms of illness? Would you like to be able to diagnose diseases of aquarium fish?

Here you can look through pictures of sick fish to diagnose diseases of aquarium fish. In the next step we will show you how you can quickly and reliably combat fish diseases and also prevent them from recurring.

To the Online Hospital

General information

About 90 % of all fish diseases can be traced back to a weakening of the immune system! The use of remedies may combat the pathogen but they generally can’t eliminate the cause! It is, therefore, absolutely essential to determine the cause. In most cases the causes can be found in the following areas:

New fish: Even when newly purchased fish do not show any obvious signs of illness, they still can be carriers of parasites or pathogen bacteria. It often happens that these “new” germs for the previous inhabitants are unknown so that they haven’t developed enough resistance to them. This situation is reminiscent of the Spanish conquest of South America, when they wiped out huge parts of the population with the cold viruses they brought with them! Please don’t always blame the pet shop retailer!

Expired food (which has been opened for more than three months). The vitamin content is then far too low. It is no longer enough for the animals to build up any resistance.

As soon as the first signs of disease become noticeable IMMEDIATE action is required. In most cases people wait too long. As an example: as soon as the smallest “spot” becomes visible, treatment needs to start. Waiting too long leads to that one little spot (white spot disease) coming off the fish’s skin, falling to the bottom and, after a capsule formation, releasing 1000 new spot pathogens, which increase the likelihood of infection spreading to all the other aquarium inhabitants.