Those are not good, but there are several ways to get rid of them, or at least keep them under control. I personally have only used a peppermint shrimp to control them. However, I spotted them early on, while they were small, and very few. There are other things like Joe's Juice that others have used, but I have not personally used that. I'm sure there are other things that will work too. Hopefully someone else will help out.
Good luck!!