04-06-2011, 05:00 PM
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Why do you think an additional filter is needed?
Just so you know, I have battled cyanobacteria. With 7 aquaria running presently, it has appeared in only 2 of them. The 10g in the window was no surprise, and it was deliberate; I was encouraging algae with strong sunlight in order to provide food to my Farlowella fry that only eat fresh algae. The old 70g was a different problem. It appeared in October 2009 and lasted until the following January; every week I removed as much as I could manually, vacuumed the substrate well, reduced light and fertilizing. Every week the same, then suddenly, gone. With near-identical conditions in 7 tanks I've no idea why cyano occurs only in one, just as I can't explain why brush algae will only appear in another.
Here is some useful info on cyanobacteria, written by Dusko Bojic. My only caution is not to jump into "cures," as these can sometimes cause other even worse problems. The antibiotic mentioned for instance will harm some plants to the point of destroying them. It is always better to find the cause and fix that.
Blue-Green Algae even though called algae, is not classified anymore as one. This "algae" is actually cyanobacteria. It forms slime, blue-green, sheets that will cover everything in a short time. It can be removed mechanically but will return quickly if the water quality is not fixed. It can be treated with Erythromycin phosphate, but this might effect the nitrifying bacteria in the gravel and filter. When the BGA gets killed by the algaecide it will start to rot and through that process it will reduce Oxygen levels in the tank. Since the nitrifying bacteria needs O2 to transfer ammonia/nitrItes into nitrAtes the nitrifying process will slow down. If algaecide is used, make sure to test the ammonia/nitrite levels. Remove all the visible algae to prevent it from rotting in side the tank. Some aquarists use the black-out method, where black bags are wrapped around the tank for 4 days and held in complete darkness. It is advisable to raise NO3 levels to 10-20ppm before starting the black-out period. All visible algae should be vacuumed before black-out and after the black out.Egeria densa (Elodea) and Ceratophyllum demersum are good plants to have in a tank. These plants secretes antibiotic substances which can help prevent Blue-Green Algae. Establishing, lots of healthy, fast-growing plants from the day you start the tank + dosing the nitrAte levels to maintain 10-20ppm (in planted aquariums) and vacuuming the gravel (in non-planted ones), is the best way to prevent this "algae". The BGA can be found in aquariums with very low nitrates because it can fix atmospheric nitrogen. BGA seem not to like very low pH and high CO2 levels. BGA doesn't prefer strong water currents. Excess organic loading is the real cause in many cases. Try removing decaying plant material and prune old leaves that are leaking organic nutrients back into the water column.