GDA is related to ammonium. Increase efficiency of your filter or reduce feeding. Wiping it off isn't very effective - GDA is flagellated, all that survive scraping will return to the glass at night.
No, the 1st time I ever saw GDA the owner had a nice wet/dry filter..........
There was no NH4.
I've dosed NH4 and have large fish populations, never was bale to keep a culture for long except for one small tank.
Anyway, the OP posted about GSA, not GDA.
GSA is fairly well understood,: higher PO4 and higher CO2(not just one but both).
GDA is NOT Chlamydomonas
, it is actually Akineoscedesmus
. If you take a sample, look under a scope, you will see this Genus. I have not found the species, I do not think it matters so much for us and it's tougher to ID.
Sewingalot has a few pics of it and her method usign EM antibiotics worked for some folks, but not others. My method of letting it be and run the course and then cleaning after 20-30 days seems to have the highest success rate, but...there are plenty of folks that still had issues.
Hard to say what causes it, the observations are pretty wide, and I am not able to induce and maintain any cultures, without being able to do that, there's little one can do to test in situ on a planted tank.
So we cannot say much about cause nor cures. Folks can try a few of the methods to cure their own issues, I really do not fuss with that, I stick to good plant growth and good care of the plants, this works better than any algae trickery in the last 20+ years I've kept planted tanks.