03-18-2008, 01:36 PM
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What you have sounds less like algae and more like Cyanobacteria. This is a fuzzy looking red algae-like growth that blankets rock, glass, substrate, and even corals if left to spread. Cyanobacteria is all too common in SW tanks and generally develops as result of excess nutrients coupled with poor calcium and degrading lighting. While cleaning your rock as you did may temporarily solve your problem, It is likely to return in short time if conditions for it's growth are still ideal. The best means to stop Cyanobacteria is to improve conditions for Coraline growth. With appropriate calcium levels, coraline will begin to grow better and faster. Coraline uses phosphates and nitrates to grow, so improved coraline growth will also boost your nutrient export. this will help to starve out the cyanobacteria. As your lighting ages, the bulbs begin to degrade, slightly altering the spectrum of light they are emitting. This altered spectrum of light begins to become more beneficial to undesirable algaes and Cyanobacterias, and less beneficial to coraline and the inhabitants of the tank. Cyanobacteria is relentless, so, while you may never fully rid your tank of it, if you strive to keep conditions optimal for Coraline growth, you should see a noticable decrease in its presence and growth rate.