green algae looking stuff.? It looked completely normal this morning and all of the sudden we noticed it at the bottom looking kind of green. All the other fish seem fine. What could be the problem and what should I do?

It is a dalmation molly in a 30 gallon community tank. There are 9 other fish... 5 platies, 3 gouramies and 1 algea eater. The fish died BTW... but I still want to know if there is something I need to do to keep my other fish healthy.