blackouts need to be at least a week or two... i usually blackout for a minimum of two weeks, if theres still algae then perhaps maybe another.
I have had a couple boughts with BGA and something in that thread was contrary to everything I had ever heard. I had always heard that high nitrates were a prime trigger (along with overfeeding, high phosphates and too much light) of BGA but according to his article, LOW nitrate is the problem. I had never heard or read that before. I'm not quite sure what the reasoning behind that is though as I always thought/heard the nitrate is what the BGA fed off of.Its blue green algae, have a look at the sticky by George a blackout is the best way to get rid of it. No reason to remove the sand, it would just return on the new sand.