Combatting algae - here’s how it works

Algae can make your aquarium look very unsightly. They can overgrow your plants and decorations and restrict your fish’s habitat. But it is not that difficult to prevent or get rid of algae!

Why do algae grow in the aquarium and what can be done about it?

When algae get out of hand in the aquarium, there are always one or two causes. In this video, biologist Heiko Blessin explains very clearly and understandably why algae grow in the first place and what we aquarists can do about it. The topic of algae in the aquarium has never been explained in a simpler and more understandable way!

Why are algae a problem in the first place?

Algae belong in the aquarium as much as other water organisms. You can’t totally prevent their occurrence. As long as the algae growth remains low or it doesn’t noticeably gain the upper hand there is no need to worry. Strong algae growth, however, has a dramatic effect on the water: Algae are plants and produce oxygen during the day. But at night the situation reverses and the algae consume oxygen. With a heavy algae infestation the oxygen can drop into dangerous ranges at night and threaten the life in the aquarium. It is then advisable to aerate at night.

Exposed to light (during the day), the algae continue to consume carbon dioxide (CO2) like the water plants. This consumption can lead to an extreme increase in the pH level (pH > 9), which in turn leads to a life-threatening environment.

If the CO2 content in the water is no longer sufficient, algae are able to dissolve the CO2 out of the carbonate hardness (KH). The result is a decrease of this important water parameter which leads to an unstable pH level. The pH level drops significantly at night (to values as low as 4) and rises during the day to far too high values (up to values over 10), and this can mean the death of the aquarium dwellers.

Finally it is worth mentioning that dying algae are broken down by bacteria during oxygen consumption. Therefore the water needs to be aerated additionally when algae die!

Why do algae sometimes grow so much?

Algae are plants and grow especially strongly when lots of nutrients and light are available. With the help of water tests you can check how much of the main algae nutrients phosphate and nitrate are present. It is important for you to find out why such a strong excess of nutrients occurred. Mostly the cause is overfeeding, an insufficient partial water change or too high fish stock combined with too few plants.

Determine the food sources of the algae

Nitrate (NO3) and phosphate (PO4) promote the algae growth in the aquarium, if the following values are exceeded:

Nitrate: 5-10 mg/l ( JBL PROAQUATEST NO3 Nitrate )

Phosphate: 0.1 mg/l ( JBL PROAQUATEST PO4 Phosphate Sensitive )

How to remove the algae nutrients

To remove nitrate in the aquarium use JBL BioNitratEx (biological long-term solution) or JBL NitratEX : immediate instant solution.

To remove phosphate in the aquarium: either with special filter material ( JBL PhosEX ultra ) or with liquid preparation JBL PhosEx rapid .

Phosphate/nitrate ratio

Scientific studies have shown that the phosphate/nitrogen ratio has a large influence on the algae growth. The ideal ratio for freshwater plants is 1:16 (converted to phosphate/nitrate it would be about 1:10).

Outside this range, which ranges from 1:15 to 1:30, the algae growth increases significantly, especially this from blue-green algae (cyanobacteria).

Do I have to use an anti-algae agent or is it also possible without one?

This is a good, justified question! If the aquarium is heavily algalised, a nutrient withdrawal is usually only helpful for a short time - and then the algae are back. The aquarium is tipped, like a scale, towards algae. It really helps to first use an anti-algae agent to tip the "scales" away from the algae tendency. Only AFTER you’ve used an anti-algae agent, will nutrient elimination via nitrate or phosphate removal work.

Combatting the individual algae species

Thread algae

Mechanical removal: wind with hose/bottle brush

Measure and, if necessary, reduce the nitrate and phosphate

Reducing algae-promoting light components: algae-promoting light components, which are hardly perceptible to the human eye, are filtered out by a very slight ambering of the water, as through sunglasses. By adding JBL Tropol to the aquarium you can achieve this effect.

Insert more fast growing plants, such as hornwort, swampweed, waterweed or Ambulia

Curb with UV-C water clarifier, which kills off the algae spores, see also UV-C

Use anti-algae agents: JBL Algol (Use biocides safely. Always read the label and product information before use. Registered at the Federal Institute for Occupational Safety and Health under BAUA number N-19236)

Brush algae

Immediate removal of infested leaves by hand. Cut off leaves at the base (simply with JBL PROCLEAN POWER )

Free technical items and decorations from algae with JBL Power Clean .

Suckermouth barbs of the Garra family (e.g. Garra pingi) eat brush algae! Amano shrimp can keep brush algae at bay but cannot completely eradicate them.

Clean “rotting areas“ in the aquarium. Always siphon the substrate with the water change with JBL AquaEx Set 45-70 or JBL Aqua In Out Complete Set .

Promoting plant growth: iron and trace element fertilisation with JBL PROFLORA Ferropol .

Limiting phosphate through JBL PhosEX ultra or JBL PhosEx rapid with very high values.

Reducing the current.

Decreasing the carbonate hardness (in hard water).

The most important step is to increase the CO2 content of the aquarium water by using the JBL CO2 system.

Using anti-algae agents: JBL Algol (Use biocides safely. Always read the label and product information before use. Registered at the Federal Institute for Occupational Safety and Health under BAUA number N-19236) .

Smear and blue-green algae (cyanobacteria)

Please note: can be confused with diatoms! Smear algae feel greasy-slimy and have an unpleasant smell when you take them off the water. In comparison diatoms feel rougher. Blue-green algae (cyanobakteria) only grow when the natural soil flora is disturbed. This can be the case for just one area in the aquarium but also for the whole aquarium. It is not easy to find out why the bacteria flora is being disturbed and combatting it can sometimes be a lengthy process.

A mechanical removal (siphoning etc.) does help, but is not a long term solution

Improving the water quality (intensifying the water change, reducing nitrate and phosphate)

JBL PROSCAPE PLANT START : spread granulate on the aquarium bottom and cover with substrate. The granulate is loaded with special bacteria, which decompose the excessive nutrients (sugar, proteins etc.) which are often the cause of blue-green algae. JBL PROSCAPE PLANT START contains mixed cultures of bacteria which colonise the substrate itself and thus prevent undesirable bacteria like cyanobacteria from doing it.

Light deprivation: A total deprivation of light in the aquarium for at least 4 days helps greatly against blue-green algae which are dependent on light for their photosynthesis. Then carry out a 50 % water change and always siphon off any new algae

Always carry out partial water change with substrate cleaner ( JBL AquaEX Set 20-45 ) instead only siphoning water

Spot algae (often young brush algae)

Mechanical removal from the panes with glass pane cleaners ( JBL Aqua-T Handy , JBL Blanki , JBL FLOATY II )

Excessive nutrients are also the main cause for these algae.

Measuring and, if required, reducing nitrates and phosphates

Brown algae (diatoms)

Please note: these are sometimes confused with smear algae! In comparison diatoms feel rough, not slimy. Both often occur in mixed cultures (dark-brown to black coatings).

The cause is the silicate content of the water (tap/well water). Use JBL PROAQUATEST SiO2 Silicate to determine whether silicate is present. If silicate values exceed 0.4 mg/l, a good silicate remover ( JBL SilicatEx Rapid ) is needed.

With high silicate values in tap water an osmosis system will help to remove 95 % of the silicate

Tricky but effective: an ion exchanger with the special synthetic resin MP 600 removes silicic acid directly. If installing an ion exchanger after an osmosis system it only needs to remove the residual quantities (5 %) of the “slipped through” silicic acid and therefore keeps quite a long time before it needs to be regenerated

Floating algae = green water

UV-C water clarifiers like the JBL PROCRISTAL UV-C Compact plus 11 W are guaranteed to eliminate floating algae (green water) within a few days. Caution: A fine filter material (e.g. JBL Symec micro ) retains the killed floating algae very well, but can quickly become clogged and needs to be replaced regularly.

Measuring and, if required, reducing nitrates and phosphates

JBL Clearol works as a flocculant and makes floating algae clump together, so that they can be caught in the filter or siphoned off

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