Oh no...it's over...drain the tank.
Just kidding, seems pretty typical to get this stuff along with other stuff you don't want. There is a ton of info on here, check out some threads. Basically you have phosphates in the tank, since you're cycling just let it go, it's actually helping you if ya think about it. It's using the phosphate to grow.
Once you're cycled this will be more annoying in size, get a phosban reactor and GFO. I had the same stuff, took the rock out and scrubbed it in some salt water in a bucket. Hooked up phosban reactor, and haven't seen it since.