| | Re: Alage problem
Without a doubt its BLUE GREEN ALGAE a bacteria and not a true algae.
Usually from polluted tanks, filters, substrate, old bulbs, wrong spectrum of lighting, high PO4 and low NO3 - very high on both, very high organics. Becareful it is an hepatotoxin (liver toxin). Dont splash into eyes or mouth, cuts and wash-up well.
You can treat with Maracyn (antibiotic) or do a blackout for 3 days. You need to clean your tank and check on all the above items first and then gravel vac well after treatment with at least a 50% water change.