WEIRD brown algae.. anything guys?

[fishman72b]

I seem to have a small breakout of brown algae. i have had this before and it took over the tank. Now it is just two blotchs on a rock and seems to be spreading... i thought this would go away if the tank had good flow.. now this is the weird part.. it is growing on the part of rock whrere the powerhead is DIRECTLY hitting! And i have a clean up crew in there. Any pointers? thanks

 

[cora]

Sounds like brown diatom algae, if so, you can usually just blow it off the rocks by using a powerhead in your hand—won't work on glass, but it easily wipes off glass. It will grow anywhere the flow from powerheads hits, and tops of rocks, on substrate, etc. where light falls on it.
If you let it get out of hand, the old dying algae will just feed new.
It's nothing serious, but ugly and annoying. The only way I've been able to get rid of it is by getting the posphates and nitrates really low or at zero.