I believe this is alge. It appeared about a month ago on the output of my canister filter and had not spread to anything else until lately. Now it has small amounts growing on the driftwood and a few select plants. It is growing on the rocks in the tank and on a my rams-horn snails. Most of it is black or dark, some of it is starting to turn bright/light green. Any one know what it is and how to treat it?