Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
No doubt GDA is an algae, along with many others.
But evidence of a symbiosis between cyano and GDA, along with finding out what I'll call "black spot" is really cyano, is interesting enough.
Thank you for the clarification and excellent pictures!
BGA is also easily reintroduced from another tank, even if you don't know you have it. For a while, every time I moved plants from my high-tech 46G to other, low-tech and less stringently maintained tanks, BGA appeared in the recipient tanks; even though there was zero visible evidence of BGA in the 46G. Treating all my tanks simultaneously took care of that, once and for all.