Hydrogen Sulfide?

Tank Specs:

16 Gallon Bow Front

Ammonia = 0

Nitrite = 0

Nitrate = 10



So, I decided to re-aquascape my tank today and I made a startling discovery. I'm still really new to everything and think I may have a slight problem. When I moved the largest piece of rock that I have, the edge was buried in the sand about 1.5 inches. As soon as I moved it I noticed the edge was dark grey in color and had the smell of sulfur. I immediately pulled it from the tank and put it in the bucket of old tank water from my water change. I was leery earlier that there I possibly could have a problem due to a lack surface agitation to keep everything adequately oxygenated... but up until now, I really was unsure since the pair of fish that I have are doing well along with all my CuC. Anyways, I immediately started researching and have come to the conclusion that I possibly have a hydrogen sulfide issue due to a possible lack of oxygen.



Here is what I have done:

I immediately repositioned my power head so that I am getting a lot of surface agitation and finished up with a 25% water change this evening. The rock is now bleached really white where it was under the sand and is in a bucket with a heater and power head. I do not have a QT tank for my lone pair of fire fish but they seem to be un affected with all of my CuC.



So my question is, what do I do now? When I put the rock back in, should I just lay it on top of the sand instead of seating it down? If I do that, How to I make sure that the rock isn't unstable?



Thanks for the help!