Brown algea, not diatoms

[20 gallon nano]

I've been battling brown algea living on my rocks for a long time.it only comes out during the time the lights go on. During the lights out period my rocks are all green until my lights turn on and they turn brown. I'm also having trouble growing purple corilline on the rock, I'm guessing this brown algea in not letting it enhabit the rocks. I'm just starting to get purple corilline on my pump, refugium walls and glass magnet cleaner. I run chemipure elete and gfo in a brs 2 canister reactor. I do water changes every other week. Cal at 450, alk at 10. Phosphate 0.I run my t-5 bulb lights for 8 hours. One more thing I had this thank up and running for a year an a half so it can't be diotoms.

 

[Afakasi831]

do you use RO/DI water? if not its probably the silicates if your water or is there an outside light source hitting your tank? also id recommend a cut down on light time until the problem is solved.

 

[Afakasi831]

sorry just read not diatoms. is it kind of fuzzy looking?

 

[20 gallon nano]

I use rodi water with 0 tds coming out into where I store it. except when i check my tds in my top off container it reads 15.its a open top container. idk if that would cause any issues.