OPWed, Jul 1, 2026, 6:33 PM·reefdad_tom·Tank: 29g biocube

Brown dust all over the sand 3 weeks in, did I mess up?

Started my first saltwater tank about 3 weeks ago. 29 gallon biocube, dry rock, bottled bacteria. Ammonia and nitrite finally hit 0 last weekend. Now theres this brown dusty stuff all over the sand and the rocks. Kind of looks like cinnamon. I scrub it off and its back the next day. Is this the diatom thing people talk about or is something wrong with my water? Using RODI from the machine at the grocery store.

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Replies4

Wed, Jul 1, 2026, 9:33 PM·saltcreep_sam
Yep thats diatoms. Totally normal for a new tank, pretty much everyone gets it. It goes away on its own once the silicate gets used up. Grocery store RO can have silicate in it though, so worth testing that water or getting your own unit eventually.
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Thu, Jul 2, 2026, 3:33 AM·nano_nat_reefs
Had the exact same thing in my 20. Lasted about 2 weeks then disappeared basically overnight. A couple nassarius snails helped keep the sand stirred. Dont add a bunch of fish just because the numbers look good.
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Thu, Jul 2, 2026, 8:33 PM·reefdad_tom
Ok good that makes me feel better. Kids keep asking when we get Nemo lol. Holding off another couple weeks.
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Fri, Jul 3, 2026, 6:33 PM·shock_orange
Smart. Cleanup crew first, then one fish, then wait. Also run your lights shorter for now, like 6 hours. Helps with the brown stuff.
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