sand and shells turning black in tank

L

lithe

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May 2, 2012
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Some BACKGROUND: I have 3 established tank and only 1 is giving me this problem. I live near a beach so I collected shells (not sand) and washed them very well and placed them in the aquariums on initial setup several months ago. I used store bought aquarium sand for the substrate in 2 of 3 of my tanks. I also treat with special blend and nite out regularly (along with prime) to avoid cycling issues (which works perfectly for me and my fish are much happier with the stinky stuff).

Anyway, PROBLEM? When I did a water change last week and pulled some of the shell/coral pieces out (which are dead), the parts that are under the sand had turned COMPLETELY BLACK. And I don't mean gray or brown. I mean, BLACK BLACK BLACK. When I placed it back in the water without touching the sand, it slowly turned brown and then almost back to usual color. That was weird.

Now, however, I'm noticing on the sand on the sides of the tank, I see swirls of black sand. What is going on?

The only other things I have in the tank are PVC pipes for hide outs, fake plants, an aquarium pot decoration and a very tall ancient column decoration. Anyone know what is going on?
 
Anaerobic and anoxic heterotrophic bacteria that colonize buried substrate often darken it or even turn it black. There's also temporary color changes that can occur from redox reactions (called a reduced matrix) that go away within minutes of exposing the buried substrate to oxygen.

ETA do you get a whiff of rotten eggs when you expose a lot of the black stuff? That's hydrogen sulfide and would confirm that's what's going on.
 
The problem is I use special blend which is the most horrid smelling solution ever. Though the smell dissipates over time, the tank still has a sulfurous odor which is the special blend. I'm not sure I will be able to tell the difference between the special blend stink and a stink from the bacteria you described. Today, I've scheduled another water change so maybe I will see what happens when I sift the sand a bit and maybe I'll take one of the shells out of the tank and give it a good sniff to see if it stinks differently than the general special blend stink of my tank.
 
Huh, I don't know anything about special blend. Based on the color change you saw, I'm guessing that has to be a least part of what's going on.

I have a deep sand bed in my tank and the whole bottom layer is dark grey-black. That's what I was going for, though.
 
I get this in my 3 gallon which has very fine white sand. When I pick up a rock it's dark grey under. I figured it was just anaerobic bacteria.

You'll know the smell is distinct from whatever you're using. Take out a rock sitting over it, which will probably be stained dark too and smell the top of the rock. Then smell the bottom. Wowwie weewah!


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This is why shells are usually not recommended in freshwater tanks. They tend to do some funky things (being made of mostly calcium carbonate and all). It sounds to me like either anaerobic bacteria or diatoms. Neither are really bad, but I don't know what to suggest to keep the shells looking white and clean. The only time I use shells are in large amounts of water (such as small outdoor tubs/ponds) where they don't seem to make much difference because they are diluted by 100+ gallons.

I think you'll find that your fish will be just fine without that expensive additive...water changes are the best thing for your tank, you really don't need "sludge eating bacteria" to keep your tank clean and healthy, water changes and siphoning detritus should suffice :) In fact, that stuff may be one reason you are having issues with your shells. Do you use special blend on all the tanks with shells?
 
platytudes said:
This is why shells are usually not recommended in freshwater tanks. They tend to do some funky things (being made of mostly calcium carbonate and all). It sounds to me like either anaerobic bacteria or diatoms. Neither are really bad, but I don't know what to suggest to keep the shells looking white and clean. The only time I use shells are in large amounts of water (such as small outdoor tubs/ponds) where they don't seem to make much difference because they are diluted by 100+ gallons.

I think you'll find that your fish will be just fine without that expensive additive...water changes are the best thing for your tank, you really don't need "sludge eating bacteria" to keep your tank clean and healthy, water changes and siphoning detritus should suffice :) In fact, that stuff may be one reason you are having issues with your shells. Do you use special blend on all the tanks with shells?
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I think we are thinking along the same lines.
 
I've noticed in a few different threads that prime and or similar products seem to be used on a regular basis. I've also been berated for suggesting that products be used for what they were intended for. I'm not saying that Prime shouldn't be used for cycling a tank but the only time I ever use it is for conditioning my tap water and in extreme cases of nitrite spikes. You mentioned your tanks are established so why are you so worried about cycling issues? Although the use of these products may have nothing to do with your issues trying to pin point the actual cause makes it more difficult by having so many variables. I don't know how shells affect systems because I've never used them in any of my tanks. But it would seem that in order to figure this out your going to have to eliminate possibilities. My philosophy has always been to keep things as simple as possible so when a problem does arise there aren't as many questions to answer. All my tanks (from reef to planted to nano) have always been healthy and relatively free of any major issues. Sometimes less is more and allowing my systems to become established with little interference has served me well for years. Not to mention my piece of mind and more coin in my pocket to spend on the things I really enjoy

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Well, I have established tanks but I still do a water change once a week to clear out debris. That is when I use Prime. I use special blend (and nite out, as recommended). It eliminates frequent water changes and keeps my tank completely stable.

Someone asked about my PH which is constant 7.6 in all my tanks. It's on the high end of what the fish like in my blue ram tank, but they are very happy and surprisingly lively fish.

Anyway, I'm not worried about the shells looking ugly. It was just alarming. It made me jump when I noticed something black. I thought I like had killed something under there and did a fish count. I was so confused. I think it is the bacteria thing because yes, it did smell stranger than the special blend. And, it makes sense because when I expose, they return to their color.
 
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