02-27-2011, 07:30 PM
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I have had bouts of about every algae there is at one time or another. Inga, you probably won't have to tear your tank down and start over. But sometimes this is needed. I am planning on doing that this week to my 90g which has got out of hand.
All algae [except diatoms, and to some extent cyanobacteria which is as Lupin said not a true algae] occurs because of excess light. Nothing else. Algae is a plant, and like all plants it needs light and nutrients. But unlike higher plants, algae can use any light, and any nutrient. Higher plants need red and blue to photosynthesize. And they need a balance of 17 nutrients, balanced among themselves and with the light intensity and duration. Provided this is all balanced, plants will out-compete algae [as Neil Frank wrote in that linked article]. Several planted tank authors have written that in a well-planted balanced aquarium, algae is never a problem; it is there, but never to the extent that it becomes problematical.
Rhonda Wilson who runs a website and writes monthly for TFH has said that in her fishroom of 50+ tanks, certain types of algae will appear and be bothersome in some tanks but not any others. She can only assume that there is some biological or chemical makeup in this tank or that tank that provides what that particular species of algae needs to increase. When it gets out of hand, a tear down is usually the best remedy.
I have noticed slight (usually) increases of algae during the summer months when more light is in the fishroom. Even with blinds and drapes, it is still "brighter" and for longer, and I am certain this is behind the algae increases. Reducing the tank lights at such times by even one hour often works to stop the increase. But not in every tank.
Old fluorescent tubes [no longer emitting sufficient intensity] can cause algae to increase. The reason is exactly the same: the light is no longer adequate, and plants slow down photosynthesis accordingly, but the nutrients are still being added so algae takes advantage--it is not fussy about light. This is another reason tubes should be replaced regularly, and long before they "burn out." Many have found that replacing tubes causes a decrease in algae. Not surprising.