Black sand under my rock!!

TracyZeuner · #1 12/19/2007, 07:20 PM

I was redecorating today and moved a rock that has been in the same place for about 1 1/2 years. Under it was some sorta black stuff that smelled BAD. I took the rock out and gave it a good rince and then vacummed the sand. Any ideas? I have never seem this before.

TammyLiz · #2 12/19/2007, 08:05 PM

I've not seen it myself but heard of it. It can happen in either fresh or saltwater setups.

Anaerobic bacteria have flourished under the rock as there was no circulation. They can remove nitrates and are the purpose of a deep sand bed in the saltwater application (do you have a dsb in this tank?) but disturbing it and allowing it to escape into your water is not good for the inhabitants, which is why a dsb shouldn't be touched.

I'm not sure if what you had under your rock was good or bad but certainly isn't good to have it escaping into the main water column of your tank either way. Cleaning it up once exposed was the best thing to do.

bertoni · #3 12/19/2007, 08:14 PM

I agree that anaerobic decay likely produced the black deposits and some hydrogen sulfide:

http://reefkeeping.com/issues/2005-12/rhf/index.php

TracyZeuner · #4 12/19/2007, 10:07 PM

Great article. That explains what my problem was, on the right side of the tank there is no problem. I moved all the rocks because I was removing a large(18in) Blue Carpet. The other side was made up of new live rocks when the tank was first started 1 1/2 years ago. The right side came from an old 60 gallon tank I had.
I do have a dsb- it it about 4 inches all around. The sulfide I found was only contained to one rock which I washed and then replaced in the tank after I removed most of the sand in the area.
It was in the back corner where there is little circulation. I moved the rocks away from the sides of the corner to try and get more circulation. And yes it did smell like rotten eggs!