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Discussion Starter #1
I have this dusty brown stuff on the substrate in my 20 long. The black sand looks as if it has a brown cap.

I thought it might be diatoms but there's nothing on the sides or any of the Cholla or rocks; just the substrate. It is easy to siphon and I've gotten it down to looking like sprinkles with only a couple of areas still pretty thick. I've been vacuuming five gallons a day.

I have a low-tech, heavily planted tank. Iron and root tabs; no Excel or CO2; occasional doses of Seachem Flourish Comprehensive. I have shrimp and CPO. Have removed most of the plants to make vacuuming easier. Parameters are Ammonia 0; Nitrites 0; Nitrates 15; KH & GH 12; pH 7.8; TDS 150.

Could this be actually diatoms and while the seven Oto and two Nerites are keeping the glass, rocks, Cholla, etc., clean the substrate is just too much for them to control?

I need to add more sand; can I just cover whatever is left or do I need to continue vacuuming until it's completely gone?

Thanks for your help.
 

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Likely it's just the mulm build-up. I get it a lot in my 20 long NPT as well and it easily builds up in that tank. What filtration do you have? I find it happens more in my tanks with sponge filters vs. HOBs and others.

Does it look like this or similar? (Not my pic, just off google)
 

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^_^ You're welcome!

Yeah, basically, if you have a sponge filter, you're going to get this regardless and regularly. Water changes always help out but really, just getting a HOB will do wonders for it if you find it unsightly. I still have it in my 45 but I haven't been keeping up with water changes which is my issue at present, otherwise, it's usually due to lack of water movement/kicking up to be sucked up into the filter. ^_^
 

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Discussion Starter #5
I have two new three-stage filters in that tank: Sponge, bio whatever they're called and charcoal with spray bars turned on high. They replaced the filters I killed by not remembering to keep the impellers clear. Apparently they were clogged by all that @#$% Duckweed.

But, Boy Howdy, am I glad to know it's not diatoms. :)
 

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Why not Diatoms? At least Diatoms go away lol Mulm doesn't >.<

I have the same issue with keeping my AquaClear 30 clean on my 29. I think I need to upgrade to something else....My bestie has an Aqueon filter with a built in skimmer which looks like it'd suit my needs, now just need to find money for it lol.
 

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Discussion Starter #7
Why not diatoms? Because they're supposed to go away and this stuff wasn't. :) Couldn't imagine what the heck I was doing that the diatoms overstayed their welcome!
 

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Yeah, i get that too in my 20 long which has a sponge filter. That's the one downside to sponge filters, they're great for bio filtration but not so much for mechanical filtration.
 

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Discussion Starter #9
I switched to one which draws the water up from the bottom and has bio, mechanical and chemical filtration. Am hoping that will work. Am using two in my 20. Keep your fingers crossed for me. :)
 

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Oh, thought you had some secret hatred for Diatoms in particular haha That makes more sense then.
 

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Increasing circulation will help as well, they usually build up in low flow areas of the substrate. too much mulm will affect your water quality. Diatoms help your water quality in large groups, keeps nutrients in control.
 
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