02-22-2005, 09:32 AM
Join Date: Jul 2004
Location: Greenbelt, MD - USA
iTrader Positive Rating: 100%
You have a breakout of the dreaded gray slime. It is a cyanobacteria similar in nature to the 'BGA' that is more commonly seen. Its proliferation is brought about by an extended shortage of nitrates. You will often see BGA shortly before it appears.
In the past, I have never been able to kill it with any antibiotics. The easiest and most effective way to get rid of it is to do a blackout. 3 days will often do the trick, but do 4 if you don't have any really sensitive plants. Before that, do a large water change.
If you have access to a UV sterilizer, you might try running one 24 hours a day for about a week before you resort to the blackout (along with water changes). If that doesn't do the trick, it can't hurt to keep it on during the period of (total) darkness. An effective diatom filter can also be an effective tool, though it rarely if ever does the job by itself.
I once got rid of it by totally rescaping and resetting the tank.
To prevent its return, make sure your plants have an adequate supply of macronutrients as Trena mentioned. It's really not any more complicated than that.