Brown soot/diatom problem

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Aquarium Advice Newbie
May 25, 2023
I’m having an insane time dealing with is… my tank is not new…it’s an established 6 month tank and every other day after cleaning it I get build up badly. All my plants turn brown and only after a week it’s unbearable to look at so I change the water about 30% when diatoms appear on the sides.

I have seachem fluorite in with root tabs and my light is on for 10 hours a day (I have tried to experiment with 6 hours) but nothing changes. I have 4 snails in my 29 gallon with 9 danios, 3 phantom tetras, and 1 neon tetra…I don’t overfeed and my filter is an aqua clear 70 gallon filter

Is it my substrate? Before I only used the gravel and it wasn’t this bad…then I thought it was the driftwood that the anubias are on leaking tannin but that doesn’t make sense either…

I’m desperate…


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Some of the stuff is blue green algae (Cyanobacter bacteria). It love red light, nutrients, low oxygen and low water movement. The problem is probably from the substrate and fertiliser.

Anubias are slow growing plants that don't need much light or fertiliser.


Clean the tank up and physically remove as much of it as possible. Do a 75% water change and gravel clean the substrate every day for a couple of weeks.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

Clean the filter if it hasn't been done in the last 2 weeks. Wash filter media/ materials in a bucket of tank water and re-use the media. tip the bucket of dirty water on the lawn outside.

Increase aeration and water movement around the bottom half of the tank.

If you have old (more than 12 months old) fluorescent lights, relace the globes and starters. Use globes with a 6500K rating (K is for Kelvin). If you have LED lights they are fine and you don't need to touch them.

If that fails to fix the issue, then the stuff at the following link kills it.
Ultralife Blue Green Slime Stain Remover
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