stringy black algea

[ajm]

My 20 long has been set up for a few months now, weekly water changes of 2.5-3 gallons. No major changes latley and all of the sudden an algea is growning on the substrate. It has a black/dark purple color and is long/stringy looking. It also grows and spreads very fast. Do you guys have any idea what this stuff is and how I can get rid of it. Pics below.

 

[BeesGoneWild]

we love pics. First guess would be dinoflagellates. But lets see some pics

 

[ajm]

They should be in the main post now. I guess as I was editing the post you had posted. thanks for the quick reply

 

[ACBlinky]

This stuff recently started to grow on the sand in my 90g as well (after we tore the tank apart to catch a few fish). I believe it's cyanobacteria; it seems to grow together into sheets which peel easily from the sandbed, and has the same soft texture as red cyano. Cyano comes in black, blue-green, green, red and possibly even other colours. Dinos are usually brown and typically grows into much longer, slimier strings IME. Either way, manual removal coupled with limiting phosphate and (to a lesser extent) nitrate will help take care of it.