[DrHank]

Hopefully the rising bubbles are free nitrogen gas from the breakdown of Nitrate. The down side is that if this is happening in the substrate it is probably from the action of anaerobic bacteria. Also, a by product of this action is the production of Hydrogen Sulfide Gas. This is toxic to everything in your tank in very small amounts.

Have you noticed any change in the smell around the tank? As hydrogen sulfide is released, it gives off a rotten egg odor.

What ever you decide to do, I would avoid disturbing the substrate which could result in releasing the gas with devastating results.