Why do I have black/grey stuff in my sand?

[Icewall42]

This is my first time using sand, so I'm really curious if this is normal. Anyhow, I was doing some replanting and pruning in the tank, and when I stirred up the sand where a bunch of elodea/anachris was planted (live plants), there was a bunch of fine, blackish grey matter in the sand that smells to high heaven. I stirred up the sand around this plot but this junk was localized to the sand where the live plants used to be planted.

What is this?? Is it just rotten plant and fish waste? Or something dire?

[hemi]

dead plants

[chefkeith]

I think they might be pockets of anaerobic bacteria. These bacteria convert matter to gas. It gives off a strong rotten egg / sulfur smell when it's released from the substrate. If you have alot of this in the substrate DO NOT stir it up. It can kill your fish. The safest thing to do is to stir the substrate regularly from day 1. Next best thing to do is to try not to ever disturb the substrate. If you have to disturb the substrate use a gravel vac or long pvc pipe and poke it through the substrate as far as you can. This will release the gas up through the gravel vac tube or pipe and not in the water column. I wouldn't do to much disturbing at one time.

In nature, these gas pockets can be huge. When they are released from the ocean floor, they have been rumored to sink ships and crash airplanes in the Bermuda Triangle.

[Icewall42]

Yikes! Well, I tried not to stir it up too much. I sucked as much of it out with the gravel vac as I could manage, so hopefully I got most of it. It also smelled strongly of what you described, though it also sort of smelled like bad swamp water.

[mistergreen]

that's the down side to using sand unless you have lots of rooted plants.

[Icewall42]

And God only knows that's a tough thing to do, given with how much glee my clowns uproot everything.