Why are my rocks turning brown??

[Christopher311]

I have a 75 gallon FOWLR tank that's been up for maybe 10 weeks. In the last couple weeks my rocks started turning brown. I've tried scrubbing it off and it doesn't work. My tank isn't cycling. I use RO/DI water and have been doing 20% water changed on a weekly basis. I've cut back on how much im feeding. I've got a sump with a wet/dry filter with filter floss/carbon/purigen and bioballs.

8.2 ph. 0 ammonia 0 nitrite and maybe 20 nitrates.

So what's goin on with my tank?

 

[Rutrag]

It sounds like diatoms, but you normally see them earlier in a tank's life. Have you already been through the diatom stage? If not, it's pretty normal to have them go nuts for a little while then die back on their own. Got any pics?

 

[Christopher311]

This rock was white a few weeks ago

 

[Christopher311]

And no, this is the first I've seen of them.

 

[Convict2161]

+1 on the diatoms. Looks better then the white rock IMO. Can't wait to get some color on my rocks in my new 8 gallon.

 

[Christopher311]

I'm hoping for colors as well. Brown just isn't one of them. If it is diatoms then I just wait it out? Or should I be doing anything in particular.

 

[TheTodd]

I have the same thing, except mine comes off...almost seems like brown dust. My scrubber hit a rock and a little cloud of the stuff flew off.

 

[Christopher311]

Yeah that's what's weird. This stuff is stubborn. Doesn't scrub off

 

[22engine]

Yeah that's what's weird. This stuff is stubborn. Doesn't scrub off

Wait it out if it is diotoms they will go away from what I have read as long as the water is good. My turbos munch on it too

 

[Fishfighter]

I've got some hard dark brown on my rocks too. I can't even scrape it off. Is this a diatom bloom or something else. Established tank