04-23-2012, 12:31 PM
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In the simplest terms, all green/red/black algae increases are due to excess light, meaning more light than the plants can use because some nutrient(s) is/are missing so photosynthesis slows or stops and the algae takes advantage of the continuing light. Now, other factors can play into this, like iron which I get to, but in general terms reducing the light (intensity and/or duration) until the algae no longer increases is the cure.
Cyano is organics related, so there is excess organic matter in the aquarium. If this is just a speck or two on floating plants, I never worry; but if it is obviously a problem, then the organics have to be addressed. I've had this suddenly appear massively with something as basic as not cleaning the filter often enough.
Back to the iron. Iron is a micro-nutrient and thus not required in large doses. No mention is made of the total nutrient fertilization you are using, and that is needed. But in my view iron should never be added except as part of a micro-nutrient package. The macro-nutrients are generally dosed moderately-heavily in high-tech systems with micro-nutrients less. There is a proportional balance of nutrients that aquatic plants need, and too much of some can cause plants to alter their uptake of others. Think of it as mixing medications when you're ill and getting interactions that are more detrimental than valuable.
Iron is connected to many algae, so I would look at reducing this along with the light perhaps; you haven't indicated if this is T8 or T5 HO, I will assume from the 40w tubes that it is T8, four 48-inch tubes over a 55g. That's bright but if you have this balanced with CO2 and other macro-nutrients it should work but may need to be reduced in duration.