Aarghh...been having some type of algae in patches on the walls of my aquarium for quite some time now. Manually removing them with an old credit card during water change only to find new small patches during the course of the week. It has a dust like texture and I was thinking it's another form of GDA but it start's off with a rust color not green. Would it really fall under GDA category?

Tank parameter's

NO3 10ppm weekly
PO4 2ppm weekly
CO2 about 30ppm using drop checker
3.2wpg @ 10hrs
CSM+b 10ml (1.5tbs dilluted in 500ml distilled water)