Its usually unstable co2.beeky said:I'm still not sure I understand this idea of "poor CO2 causes X algae". If this statement were true, then every low tech tank (i.e with no additional CO2) would always be plagued with algae. It must be some sort of ratio/relationship with CO2. I have hair algae in a low tech tank lit with two T8 tubes. I definitely have poor CO2 - I don't add any.
I had a hell of a time trying to control algae in my low tech tank, but then Clive suggested I do very little or no water changes at all. The fresh water will contain higher levels of co2 and o2, upsetting the balance of the tank. Plants hurry to use this like a drug addict... and like a drug addict, when the fix is gone the plants fall apart which causes ammonia and algae.