Join Date: Mar 2007
Location: Hendersonville, TN
Mmm....hydrogen sulfide! Poisonous to plant roots if it remains in contact with them for any longer than a few days. It will kill the roots, turning them black and rotten.
If you have a lot of soil in there (greater than 3") you may want to remove some. Extra soil tends to trap this gas and "hold" it in the substrate. Removal of some of the soil would help some. Still, the issue is that you soil isn't getting enough oxygenation for the water. Chop sticks or skewers can help get rid of the gas pockets (as suggested by stevenjohn), or you can use your hands to move the substrate in large areas at a time. I found this to be a more efficient way to remove the gas bubbles. Kind of gently move the substrate en mass, and it should help dislodge gas pockets over a larger area.
This will continue until your organic matter finishes decomposing. Time will take care of the root cause of the issue. Usually means that you will be moving the soil for about a month or so. Over time, you will want to do this every few months to prevent compaction, which can trap organic matter in the substrate and cause sulfide gas build up even in mature systems.