Hey George -
I agree with the majority on here... but have one little thing to add.

Do you have any plants in your tank or sump/fuge?
I was having a serious hair algae & bryopsis problem this summer, then I added a few mangroves to my nano tank. I also did the whole wc & add critters bit, as well. It cleared up pretty quickly, thankfully, and hasn't been back since!

I think I saw a rule somewhere that the average was 1 mangrove pod/per 10G of tank volume. I have 2 in 10G nano... just as a reference.

HTH

DAB