Algae prevention in your planted tank


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Nuisance algae is perhaps the planted tank owner's worst enemy. George Farmer looks at how to prevent and treat this menace.

Look at any planted aquarium Internet forum or message board and you will soon notice a question about algae. Over half the queries I receive from PFK readers are algae related.

Why is this problem so common in planted tanks? Quite simply most algae love light and nutrients, just like plants. This does not sound good — but do not worry.

Take a few simple steps and algae problems should rarely be an issue. I say rarely because the vast majority of planted tanks will suffer from algae outbreaks at some point — even mine!

Some is perfectly natural and you should not be concerned with minor amounts. If it doesn’t spoil the overall effect of the aquarium there is no need to worry. Indeed, if you have herbivorous inhabitants, algae forms a vital part of their diet.

Prevention is best…

Preventing algae from the day the planted tank is set up and maintaining it effectively is the best way to ensure algae problems do not take hold. Algae’s biggest trigger is said to be ammonium/ammonia, so ensuring these nitrogen compounds are minimised is a major factor.  

This should be achieved by a combination of effective biological and mechanical filtration, dense planting with fast growers, suitable non-excessive lighting and appropriate nutrient management via substrate and liquid dosing.

Fishless cycling is a good idea before adding lighting, plants and fish. This allows sufficient beneficial bacteria to build in the filter and substrate, helping to deal with any ammonia spikes, and this in turn helps to prevent algae. 

Once the filter is mature and the tank is planted heavily, aim to cover around half of the substrate with fast growing weeds — and adding an algae crew is a good idea. I recommend Otocinclus and algae shrimp for smaller set-ups. Siamese algae eaters (Crossocheilus siamensis) and Bristlenose are effective in larger aquaria.

High or low tech?

Establish a maintenance routine based on your set-up. Higher-tech tanks with high lighting levels, CO2 injection and frequent nutrient dosing will require a lot more maintenance and cost than a lower-tech tank, so bear this mind before you even buy the gear. If choosing a hi-tech system ensure your filtration system is suitable.

A lot of algae issues occur due to poor circulation levels in highly-lit aquariums as the nutrient demand is so much higher, but the water may not be distributing the nutrients and CO2 sufficiently. In such set-ups I recommend filters rated with around 10 X turnover: so a 120 l/26 gal aquarium should be filtered with a 1,200 lph rated external canister filter.  

Boosting circulation via powerheads is another option for those with smaller filters. CO2 injection and regular macro and micronutrient dosing is essential in tanks with high lighting levels so that the plants are fed sufficiently, allowing them to utilise all of the light instead of the algae.   

Aim for 30ppm CO2 using a CO2 drop checker filled with a reference 4 KH solution and pH reagent that turns green with good gas, blue with too little and yellow with too much. Turning the CO2 off at night is a good idea to save on gas.

Solenoids fitted to pressurised systems linked to the lighting are ideal. I generally have mine turn on the CO2 an hour before the lights go on and then off an hour before lights go off.

Daily dosing of nutrients is preferable to larger weekly doses. There are plenty of decent off-the-shelf products available that contain all the required elements — including nitrogen, phosphorus and potassium (NPK), such as Tropica Plant Nutrition+ and the Easy-Life range.  

Changing frequency

Water changes in hi-tech set-ups generally need to be frequent to help prevent algae. Changing one-third to a half per week is ample for most tanks, but consider more frequent changes for nano aquaria.

Things become a lot simpler in low-tech tanks with lower lighting levels. These significantly reduce the risk of algae with no need for CO2 injection or heavy nutrient dosing.

Typically the substrate will be nutrient-rich, allowing the plants to obtain their required food from the roots.

Circulation levels do not need to be high, as the demand for water column nutrients is reduced.

Water changes can be minimised too. In tanks with non-gas injection, liquid carbon supplements are ideal for boosting plant growth. Easy-Life Easycarbo and Seachem Excel contain a compound that also acts as an algicide, as well as boosting plant growth — but do not overdose these products.

There’s considerable anecdotal evidence that nitrates and phosphates do not cause algae in a heavily planted aquarium. In highly illuminated tanks with CO2 injection the dosing of these nutrients is considered essential to help prevent algae. If nutrient deficiencies occur, plants will leech ammonia/ammonium that can trigger algae outbreaks. For this reason, you may notice that suffering plants are often covered in unsightly algae.

Estimative Index

The Estimative Index (EI) relies on ‘overdosing’ the tank with a host of nutrients to ensure deficiencies cannot occur, thereby helping to prevent algae. There are many varieties of EI dosing, ranging from dry chemicals to relying on off-the-shelf products. Any regime relying on regular nutrient dosing with water changes to ensure nutrients do not build to excess is effectively EI.

Types and treatment of the most common menaces

There are tens of thousands of species of algae, but we only regularly experience around ten in our freshwater planted tanks.

Here the most frequently encountered types with my tips on dealing with them:

Black brush/beard algae (BBA): A species of Audouinella, this is classed as Red algae or Rhodophyta. It grows in tightly-formed black clumps of very fine hairs, hence the common name. It often grows on the edges of slow growing leaves or your décor/hardscape.  

I have never experienced its growth on fast-growing species.

In CO2-injected tanks with high lighting it is a symptom of fluctuating gas levels and/or poor circulation. In lower lit set-ups with non-CO2 it can be caused by fluctuating gas levels associated with water changes.  

Scrubbing it away is sometimes impossible, so affected leaves may need to be removed. Bleaching the hardscape will remove it, but ensure the décor is thoroughly washed and dechlorinated before re-installing in the tank. Spot dosing with Easycarbo or Excel works well.

Dose the BBA directly with a pipette with the filter turned off temporarily. Do not overdose. Crossocheilus siamensis are one of the only known fish to eat it, but may do so only if hungry enough.

Blue green algae (BGA, cyanobacteria, slime algae): This is not actually algae but a photosynthesising bacteria called cyanobacteria. It grows in sheets across the substrate and plants and is noticeably bright green/blue in most cases, ranging to almost black.  

It has an unpleasant smell and starts in the substrate, spreading very quickly if conditions allow. Typical triggers include excess light hitting the substrate/glass, poor substrate and filter maintenance, poor circulation and, in some set-ups, very low nitrates.  

Manually remove as much as possible, followed by a filter clean and 50% water change, then black out the tank completely for 72 hours, ensuring CO2 injection is turned off with added surface aeration.

In the longer-term, to prevent re-occurrence of BGA, improve water circulation and, if possible, black out the substrate/glass. Consider adding more nitrates if the tank is heavily planted and the nitrate level is very low.

Brown algae: Very common in new set-ups and usually linked to early ammonia spikes undetectable via test kits. It will usually disappear in a few days/weeks once the tank has established.  

Otocinclus will relish the softer varieties and algae shrimp will usually eat the filamentous types, but ensure you have a mature filter before adding algae crew.

Filamentous algae: This is a generic term for a host of algae common in all types of set-up. Common species include Cladophora, Oedogonium, Rhizoclonium, Spirogrya (pictured above) and Staghorn.

Poor CO2 and circulation levels in tanks with high lighting usually trigger these types of algae, as does poor nutrient dosing — NPK.  

Giving the tank an overhaul or ‘re-scape’ can often trigger these types of algae, especially if insufficient water changes were performed afterwards.  

Some algae eaters will eat these if hungry enough and regular dosing of Easycarbo or Excel may help. Manually remove the affected leaves and consider revising CO2 and other nutrient dosing.

Always perform at least a 50% water change after any major tank maintenance/plant uprooting.

Green water: This is single-celled algae free floating in the aquarium water, resulting in anything from a greenish tinge to a pea soup effect. Ammonia is the primary cause, even tiny spikes that remain undetectable via regular test kits. A 72-hour blackout, followed by regular large water changes, do help, as well as UV sterilisation or diatom filtration.

Algae that’s deliberate!

Note the images with this article. Almost all were taken from the same 60 l/13 gal tank I knew was going to be stripped down. To help prove a point I doubled the lighting intensity, stopped CO2 injection and fertiliser dosing, and deliberately overfed the fish. The result after a few days? Lots of algae!

This item was first published in the March 2009 issue of Practical Fishkeeping magazine. It may not be reproduced without written permission.