Checklist: water values in the pond - how to keep it crystal clear and algae-free

Nowadays there aren’t many topics everyone can agree on, but when it comes to garden ponds, whether koi, fish or biotope ponds, everyone wants healthy fish, clear water and, above all, no algae!

But how do you reach these three targets? One year it works out without much effort, the next year you slide from one crisis to the next. So what can the causes be?

If you increase the fish stock, the water pollution caused by the animals also increases. But even without an increase in stock, the load increases, because after all, your fish are growing and with them their demand for food is increasing. With a well-dimensioned filter technology, however, you can still keep everything under control. But even without great technology, the balance can be maintained with strong planting and water movement. Water changes, either targeted to one area or at regular intervals, can help to restore the balance once it has been lost. You can read more about this in this blog post: The Water Change In Ponds Is Important!

You can see how important your helping care is, and that not everything happens on its own, but there are lots of aids to help you. You will find a summary of which factors need to be checked and monitored at which time of year in the Themeworld Pond under Seasonal maintenance .

Better safe than sorry

Imagine we had a maintenance checklist and all we had to do was stick to it to have no more algae or other problems. Sounds good, but life’s not like that. Besides the factors mentioned, the problems are generally all related to the weather and to the nutrient input from the environment. Heavy rainfall causes particularly large fluctuations in water parameters within a short period of time (more on this under: Heavy rain – watch your water values ) leading to the dilution of vital minerals and thus the danger of a sudden drop in acidity.

But please don’t think that pond maintenance is no fun and best left well alone - the opposite is true. Even without a crystal ball, there is a very simple way of seeing the future and the current status well before problems arise. Just like with a large blood count where your doctor takes a sample of your blood, you can take some water from your pond and test the water yourself, without any further knowledge of chemistry or the need for a lab. Not only is it accurate, but it can be done in a matter of minutes. The water values tell you everything about the pond’s condition and help you to recognise changes and start with countermeasures at an early stage. If you are diligent here, you’ll meet and keep all three targets from above!

With a test kit, such as the JBL PROAQUATEST LAB Koi , you can determine all relevant water parameters. The small model   JBL PROAQUATEST COMBISET POND gives you the most important water values and can be flexibly extended with individual tests from the cheaper refills if necessary. Each test kit contains detailed instructions on how to carry out the test, record sheets to document it and information on the correct range of values and possible actions to take if the values are too low or too high. Glass cuvettes, syringes and reagents are included for an immediate start.

How often and which water parameters should you determine? What range of values is okay and what do the individual parameters actually mean?

Basic measurement - test once a week

You can determine the following four parameters together in less than 3 minutes. Testing at least once a week, keeps you on the safe side and prevents diseases and algae problems. If the pond environment is stabilised and sufficient minerals are present, there is no danger for the pond inhabitants.

In detail - t, KH, pH and GH

A stable pH value between 7.5 and 8.5 is not just beneficial - it also ensures the safety of all the aquarium’s inhabitants and biological processes. With their rapid assimilation during photosynthesis algae consume the hydrogen carbonate in the water and this results in the effect of biogenic decalcification. Due to the lack of KH, the pH value is no longer sufficiently stabilised and can drift up to heights dangerous for fish (above 10) or fluctuate strongly. That’s why a sufficient carbonate hardness is advisable and should be at least 5 °dKH.

The general hardness is often neglected in the garden pond. Dilution effects can occur after heavy rainfall and the resulting imbalance needs to be compensated for. Values that are too high mean it’s time for a water change. We recommend a range between 5 - 30 °dGH.

In winter, it is important that the temperature in the pond does not fall below 4 °C. It’s a well-known fact that the water layers prevent this from happening, so when the water surface seems about to freeze it’s your final warning to stop mixing the layers and to switch off the pumps. In summer you need to compensate for temperatures above 30 °C by stopping the feeds and providing an additional oxygen input along with strong surface movement. Simple sun sails help to provide the shade to cool the water sufficiently.

Value - determine with Recommended Increase value Decrease value
t (°C) - JBL Pond Thermometer 4-30 not necessary more water movement
KH - JBL PROAQUATEST KH Carbonate hardness 5-20 JBL StabiloPond KH not necessary
pH - JBL PROAQUATEST pH 3.10-10.0 7.5-8.5 JBL StabiloPond Basis JBL StabiloPond Basis
GH (°dGH) - JBL PROAQUATEST GH General hardness 8-30 JBL StabiloPond Basis not necessary

Sick fish - test regularly and when problems occur

Don’t wait until your fish fall ill. It’s best to check the following four parameters regularly, several times a month. It takes less than 20 minutes. If problems have already cropped up, you definitely need to check the oxygen, copper, ammonium and nitrite.

In detail - O2, Cu, NH4 and NO2

When installing ponds, but also when adding water to the pond, always make sure you use copper-free metal objects. Copper quickly forms water-insoluble compounds that are deposited on the ground. This is where the problems arise, because tests only detect copper dissolved in water. A controlled copper input occurs when using medications to treat parasitic fish diseases, and with some anti-algae agents. The copper concentrations in these can be tolerated by the fish for a limited time, while the parasites etc. die off.

All creatures that live in water need oxygen for their respiration. The "invisible helpers", the cleansing bacteria, also depend on a sufficient oxygen content for the conversion of ammonium to nitrate. You can create the oxygen supply they need by planting adequately. Ponds with little or no planting need technical equipment to keep the oxygen content at the correct saturation value at all times. This can involve using stronger pumps (pond filters) in combination with a waterfall or watercourse. The saturation value depends on the water temperature.

The assimilation activity of pond plants means they can exceed this saturation value. Thus, in well-planted ponds towards the end of the sun phase, values can be found that are 1 to 2 mg/l above the saturation value.

All organic substances (food and plant remains, fish excretions) in the pond go through these stages when they decompose: proteins -> ammonium -> nitrite -> nitrate. Specific bacteria are responsible for each sub-process. By measuring the ammonium, nitrite and nitrate at each intermediate stage, conclusions can be drawn about the how well the system is “functioning.” For example, medicines to cure fish diseases can disturb the beneficial cleansing bacteria and thus lead to an increase in the ammonium and/or nitrite content. As a rule, ammonium and nitrite will not be measurable in a properly designed garden pond. Ammonium is also a plant nutrient and is not normally toxic to fish in low concentrations. Depending on the pH value, however, toxic ammonia (NH3) can be formed from the ammonium ion (NH4 +). For this reason, a pH measurement should always be taken with the ammonium measurement.

Similar to ammonia, nitrite is a strong fish poison. Depending on the sensitivity of the fish species, concentrations between 0.5 and 1 mg/l (ppm) can start to have a lethal effect. When temperatures drop in the colder seasons, the activity of the cleansing bacteria also decreases. If you then feed food with a too high protein content, a dangerous increase in nitrite can occur. At low temperatures it is therefore particularly important to use food with a high energy content (fat content) but low protein, such as JBL PROPOND WINTER M .

Value - determine with Recommended Increase value Decrease value
NH4 (mg/l) -  JBL PROAQUATEST NH4 Ammonium 0.1 not necessary JBL BactoPond , JBL StabiloPond Basis
NO2 (mg/l) -  JBL PROAQUATEST NO2 Nitrite 0.1 not necessary JBL BactoPond , JBL PondOxi-Set
Cu (mg/l) -  JBL PROAQUATEST Cu Copper 0.05 not necessary partial water change, JBL BiotoPond
O2 (mg/l) -  JBL PROAQUATEST O2 Oxygen 6-13 more water movement, JBL PondOxi-Set not necessary

Algae - test regularly and if problems arise

Green water, brown greasy deposits, dust-like green flakes or a green algae layer - the variety of possible algae is huge. The cause can usually be limited to a few nutrients and sustainably eliminated with a smart approach. Using anti-algae agents may lead to a yo-yo effect. Most people who "only" use an anti-algae agent notice that the quick results are only short-lived. Without the stabilisation needed beforehand and the subsequent limiting of nutrients, the problem will not be solved. You can find more about this under Combating algae .

In detail - NO3, PO4, SiO2, Fe and conductance

In heavily stocked koi ponds without a substrate and a sufficient swamp zone, nitrate levels can skyrocket. The heavy planting that serves as a plant purification system is missing. Nitrate-containing fertilisers from the surroundings (the bed or surface water at the edge of the field) may also be entering the pond. Excessive nitrate levels promote undesirable algae growth if phosphate as well as nitrate is present in the water. The nitrate content therefore shouldn’t exceed 5 mg/l and ideally, it shouldn’t be measurable at all.

It’s important not to underestimate how much pollen in spring or garden fertiliser from the pond surroundings can cause the phosphate content to increase. The unnaturally high nutrient supply can result in an explosion of algae growth. Algae can store phosphate in considerable quantities and thus continue to grow unabated for some time even after the phosphate content has been reduced. The sooner rising phosphate levels are recognised, the more likely it is that an algae plague can be averted. In the garden pond, values below 0.1 mg/l need to be maintained, and it is better still if they are not measurable at all.

Silicon is one of the most common elements on earth. As silicate rock weathers, silicon is washed into the surface and groundwater in the form of silicates. There it serves as a nutrient for diatoms, some aquatic plants (e.g. hornwort) and siliceous sponges. Since silicates are non-toxic, there are no limit values set in the Drinking Water Ordinance. Tap water therefore contains varying levels of dissolved silicate depending on the region.

Iron is an indispensable trace element for plant and animal organisms. Iron is crucial for good plant growth, but should not be present in too high amounts. If it is, there will be a risk of iron precipitation and danger for the pond inhabitants. Using water from wells can result in especially high iron levels.

Although the conductance has no direct effect on the formation of algae, it can indicate whether there is a problem with too many substances dissolved in the water. These can include fertiliser salts from the environment, or a too high water contamination caused by excessive excretions. You could look on it as a rule of thumb indicator for the purity of the water.

Value - determine with Recommended Increase value Decrease value
conductance μS/cm 300-1200 - -
NO3 (mg/l) -  JBL PROAQUATEST NO3 Nitrate 5 not necessary partial water change
PO4 (mg/l) -  JBL PROAQUATEST PO4 Phosphate sensitive 0.1 not necessary JBL PhosEX Pond Direct
SiO2 (mg/l) -   JBL PROAQUATEST SiO2 Silicate - not necessary not necessary
Fe (mg/l) -  JBL PROAQUATEST Fe Iron 0.2 JBL FloraPond partial water change

Miscellaneous - testing in the pond

You can determine the water at home simply and accurately, without expensive technology and chemical test set-ups, and the same applies for the following parameters. However, these do not play a significant role in the pond world:

  • Density and salinity are important for saltwater habitats. An unwanted increase in salinity is quickly noticed by the conductance. Potassium K (mg/l) is an important plant nutrient and is contained in almost all fertilisers. Since fertilisation in the pond is only done using solid fertilisers, there will be no increase in the free water.
  • Magnesium Mg (mg/l) and calcium Ca (mg/l) are important minerals for the growth of fish and for plants. They are measured separately in marine water for coral growth. In the pond, it is sufficient to measure the general hardness GH (°dGH).
  • Carbon dioxide CO2 (mg/l) is an important component for the growth of our plants. In the enclosed aquarium system it is added artificially. In a pond, as a partially open system, the large water surface enables enough to enter for underwater planting. The marsh plants make use of the atmospheric air.

Recommendations for action - increase and decrease values

In the ideal situation, you determine the water parameters, everything is within the normal range and you don’t need to do anything more. But it is important to note the date and time of each measurement, as a proper documentation of the water values helps to evaluate problems afterwards and to recognise changes over many weeks more easily. For this purpose, we have the water analysis sheet to download: ProAquaTest protocol analysis .

In the tables above, and also on the back of the water analysis sheet, you will find additional suggestions what to do if a water value needs to be increased or decreased. If you use JBL PROSCAN , you can manage the measurements digitally under My Analyses and add any further notes manually.

© 08.08.2021
Matthias Wiesensee
Matthias Wiesensee
M.Sc. Wirtschaftsinformatik

Social Media, Online Marketing, Homepage, Kundenservice, Problemlöser, Fotografie, Blogger, Tauchen, Inlineskating, Aquaristik, Gartenteich, Reisen, Technik, Elektronische Musik

About me: Seit Teenagerzeiten mit Aquarien in Kontakt. Klassische Fischaquarien, reine Pflanzenaquarien bis hin zum Aquascape. Aber auch ein Gartenteich und Riffaquarien begleiten mich privat im Hobby. Als Wirtschaftsinformatiker, M.Sc. bin ich als Online Marketing Manager bei JBL für die Bereiche Social Media, Webentwicklung und der Kommunikation mit dem Anwender der JBL Produkte zuständig und kenne die JBL Produkte im Detail.

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