Oto's knocked it back heaps, IMO it more from knocking it around before it got a chance, plus live bacteria solution overdose (I get it for free)
also maybe find some freshwater shrimp (they munch it like there's no tomorrow)
increasing CO2 and decreasing light doesn't sound like a good idea.....
had a similar problem with a Cichlid tank, used Bioballs (Concentrated live bacteria) (love it when testing a new product actually works)
cleaned it up in 1 month, in 2 months the brown stuff covering all flat surfaces had all but disappeared.
now have only one or 2 puffs of BBA every now and then