Problem Help Please

if the underside of your sand has black then dont touch it, the black is hydrogen sulfide and will wipe out your tank. if its brown then its diatoms, no big deal.

 

The fish in teh tank will dig the sand how they want, blowing it with their tails. A deep sand bed can create some nitrate problems in the future if you don't have sand burrowing cleaners. I use a 3" sand bed myself.
Are you using saltwater from the LFS? If you are using that as topoff water to replace evaporated water, you are increasing the SG of your tank. Make sure you are using plain RO/DI wter for top-off, not LFS mixed water to keep the SG the same.