My Sand Is Turning Black? Help

Discussion in 'Freshwater Substrates - Gravel, Sand' started by Anna Christine, Jan 14, 2019.

  1. Anna ChristineNew MemberMember

    So, I've had this tank for a couple of months and everything seemed to be going fine. But now the sand in my tank is turning a Grey/Blackish color. The weird thing is that it seems to be located only in the center of the tank? Anyways, my question is what is this stuff? How to I get rid of it and even more importantly how do I make sure it never comes back?


    It's been a couple days and I decided to do nothing. The black coloring is gone completely from the side and almost completely from the top now. The magic of aquariums. :woot: Thanks for all of y'all's input.

    Last edited: Jan 16, 2019
  2. Momgoose56Well Known MemberMember

    Do you have fish in there? It's probably the bacteria your tank needs. I'd leave it alone. If you absolutely can't stand the way it looks just siphon it along that visible front edge of your tank and lightly on the top and leave the rest to do it's job! Another thing that can cause staining or black sediment is high iron or manganese levels in your tap water. Neither which are harmful to your fish. You can contact your water provider (unless you are on a well) and ask them. :)
  3. Anna ChristineNew MemberMember

    I have one betta fish in my tank, as well as some ramshorn snails. I was concerned that it was something harmful to my fish. But if it's just bacteria than I guess I have nothing to worry about. But thats a releaf. I guess it makes sense where it's located then, since the snails and fish eat in that general area. Also the other day cleaned my filter media for the first time in a while. And it appeared after that. So I suppose it could be related. Thanks for your response!
  4. Viriam KaroWell Known MemberMember

    I think it has something to do with anaerobic bacteria developing. Is your sandbed pretty deep? I used to have light colored sand, which was approaching deep sand bed deepness, that would start turning black/gray starting at about a centimeter below the surface. When I did a water change I would rummage around in the sand and pull up the black stuff, and it would decolor after about 30 minutes at the surface.

    That's an interesting point; I had never fully figured out what was going in mine except that I smelled it one day out of concern and it smelled slightly metallic. My understanding of the DSBs at the time was that the anaerobic bacteria produced iron and such, which the plants then used, so I just went with it.
  5. Anna ChristineNew MemberMember

    I think my sand bed is about an inch deep. I don't know what qualifies as a deep sand bed though. If the anaerobic bacteria produces iron and the iron is what causes discoloration in sand, it would explain why the area turning gray seems to only be located in the center front. Because I don't have any plants planted there whereas I do in the back and sides of my tank. Although all my plants are water colum feeders, and there are only like 3 of them so I'm not sure that would actually make any difference.
  6. Viriam KaroWell Known MemberMember

    Fascinatingly, if I looked at the underside of my tank, the millimeter or so around the plant roots were also pale colored. So there could be something to that. Do you have access to the underside of your tank? Like, is it on the kind of stand that is not solid top?

    DSBs are usually 4-6 inches, so it might be a different process. The deeper areas of my sandbed got darker than the shallower areas, though, and I certainly didn't maintain it like an actual DSB.
  7. Anna ChristineNew MemberMember

    My tank is on a wooden dresser so I have no way to look at the bottom. The sand around your plant roots being lighter is very interesting though.
  8. Momgoose56Well Known MemberMember

    Bacteria don't produce iron. There ARE bacteria that react with iron (or manganese) to produce rust (metal oxidation) though. Iron is a metallic element and mineral. It's present in soil, every cell in the human body, plants use it and it may be in some sand sold for aquarium use. Many water sources contain variable levels of trace minerals and in high enough levels can cause water discoloration and stain surfaces as with iron, manganese and copper. Minerals can also cause water to have sometimes unpleasant odors as with iron and sulfur. The dark layer under the substrate is most likely undissolved waste along with bacteria. The only place true anaerobic bacteria grows is in a vacuum or where there is no oxygen. Botulism is one such bacteria. The bacteria that oxidizes ammonia is anaerobic it can grow in the bottom layer of aquarium substrate if left undisturbed. The reason you see whiter (or 'cleaner' areas) around plant roots is most likely because plants 'exchange' ammonia for nutrients. Here's a great article on why you NEVER want to 'stir up' or deeply siphon your sand bed:  
  9. Anna ChristineNew MemberMember

    Wait never sir up your sand bed? I'm going to have to read that because that's like the exact opposite of everything I've ever read on sandbeds.