[rachaellee]

This showed up a couple weeks ago on my sand only, not on plants or hardscape. I blacked out my tank for 3 days to try to get rid of it and the algae actually spread while blacked out with cardboard. And my tetras looked pretty bad, barely moving and almost no color at all. So I removed the cardboard and turned lights back on. I waited a few days till all my fish looked healthy and used chemiclean for cyanobacteria. The algae seems unfazed. However, I didn't remove my purigen when I treated with chemiclean. I can remove the purigen and try again, but I don't want to if this isn't actually BGA. Advice?

 

[Asteroid]

Yep, looks like BGA. Usually occurs when bio-filter is immature/weak to deal with organic load.

 

[rachaellee]

Yep, looks like BGA. Usually occurs when bio-filter is immature/weak to deal with organic load.

Shoot. About 3 weeks ago I got a new filter and I just tossed the bio-filter out of the old filter because it wouldn't fit in the new one. It somehow didn't occur to me that I probably shouldn't do that...