Sand turning black what is this?
The sand in my 29 gallon planted tank is turning black. It has only been set up a month. It's completely cycled and planted low tech plants and set-up. I don't think it's because there's anaerobic problem because when I planted it I moved sand all over and there was no black sand. I had peacock cichlids quarantining in there and they moved sand all around and stirred it up all over. I planted it one day and in the same day I moved the peacocks out and moved kribs, cories, and a molly into it.
It's been just about a week and now since I planted it and all the sand got turned over and I noticed that the sand has turned black under the surface only around the plants. Any sand not surrounding a plant isn't black. I took a look at the roots and they're not black.
So why is the sand turning black? What's going on? Is this harmful to my fish? What do I do does anyone know? Any feedback appreciated
A photo or two would help to confirm, but from your description I would surmise the "black" is not the sand itself but the accumulation of organics. This is normal and in fact wanted. Fish waste and other organic matter will settle on the substrate and work its way down into it. Bacteria then break down the organics into nutrients. Malaysian livebearing snails are helpful in this process, and so are any snails; these break down the larger bits into smaller particles that the bacteria can more easily handle. MLS also burrow throughout the sand, adding further benefit.
Another point is the colour of the sand. If you have white or very light coloured sand, you will likely see this more easily. With darker sand it is next to invisible. Substrate fish also factor into this, and you mention corys; they help by eating any bits of food that would otherwise fungus and add to the organics.
My comments are assuming what you are seeing is comparable to the build-up of dark gray/black matter along the front glass, just below the surface of the substrate.
Keeping the organics down is important; not overfeeding, and a fish load balanced to the aquarium (water volume and plants) is needed.
Another possibility might be very dark green slime, called cyanobacteria. If organics are high, this can occur, often among floating plants closer to the light source but it is also capable of covering parts of the substrate. This film would be easy to dislodge as a sheet.
Thank you for the help! Yes actually it is more dark grey than black. I would think it's organic waste but it's not found all over the tank. There isn't any up against the glass, looking at the glass the sand is all tan. If I dig a hole away from a plant, the sand is tan. But if I dig a hole right next to a plant it's grey/black. So that makes me worry. Also all the surface sand is tan, it's just the sand under the surface sand that is turning black, only around the plants. I also have clay and root tabs in the sand but I don't think those would be turning it black.
The only fish in the tank are 2 small kribs, 3 cory catfish, and a recovering small peacock cichlid. I plan to move the peacock eventually and add more cories and a cardinal tetras school as I get more plants. As small as the fish are now I don't think they would be producing too much waste. Also I only feed them once a day and they eat it all in a few minutes. I'm new to planted tanks so also new to keeping the stock low so I'm not really sure what is too much.
Now I have a 180 gallon sand tank that was set up the same day and completed the cycle at the same time yet has waaay more fish in it, no plants, and that has no black sand anywhere. So that makes me wonder maybe it's the plants making it black or something.
I'll take a picture for sure tomorrow
I've had something that sounds like what you're describing. I get dark blotches of sand around decaying roots and under driftwood. I considered this to be normal decomp. For aesthetic reasons, I would just mix the sand a bit after I moved the wood or plant. Its never caused a problem for me, my fish are healthy. HTH!
Thank you for the help! :) My mom has had my camera so I wasn't able to get any pictures and now I don't see the need to as I agree I don't think it's anything bad. I read that the anaerobic problem would smell bad and there's no bad smell coming from the fish tank when the black sand is stirred up so I've just been pushing white sand over it.
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