Black Algae??

I recently noticed small black spots on my gunite. And they grow. From what I've read it seems like black algae. They are very tough to brush away (metal brush). I've tried shocking the pool to no avail. Is there a sure fire way of ridding my pool of this stuff. My chemicals are in balance. 10k gunite with SWG in Texas. I added the salt generator a little over a year ago because green algae was driving me crazy. any help would be appreciated.
Thanks

Post a complete set of current water testing results. That will help somebody better be able to help you.

Might want to read through this thread

http://www.poolforum.com/pf2/showthr...ht=black+algae

but posting a current set of test results will also help us to help you better.

Janet

Thanks,
I'll check out that link. And I'll post my pool chemistry as soon as the rain stops here.
Thanks again.