Has anyone else dealt with this plague?
Forum searches and Google reveal a few threads alluding to it as a "mystery algae" but none seem to pinpoint what it is. It is kind of like a mix between diatoms and cyano in appearance, being a dark grayish-black slime that attaches to plants and rock but doesn't sheet like cyano. It gets covered in bubbles and often dislodges and floats around the surface. It grows back within a day or two after siphoning it all out during water changes and seems to recede a lot at night. Also, it's presence quickly leads to mass snail die offs.
Being a reef keeper as well, I recognize it as dinos as they are a much more common problem with reef tanks and have the same appearance and symptoms.
To fight them, I have raised my CO2 levels and increased my EI dosing and started substrate feeding with buried osmocote. Once those were all at ideal levels and the Crypts that the tank is full of started taking off again, I tried Maracyn treatment for a week with no effect. I tried Boyd's ChemiClean which works wonders on saltwater, but again no luck. Peroxide killed it back, but the amount of peroxide it took also triggered a massive melting of the Crypts. The Crypts have grown back, but so have the dinos. My next course of action will be a total blackout for a few days, and hopefully that at least takes it back.
I did my weekly 50% water change today and will post pics in a day or two once it has grown back to show what it looks like. Thankfully I only have it in one tank and don't share tools/equipment between tanks!