Diatoms are usually all over the sand too (at least whenever I've had them starting a tank). Could it just be algae? Different CUC members eat different thinks...I don't usually have them, so I don't honestly pay much attention to who does what, but I believe that turbo and margarita snails eat film algae. Hermits usually go after hair algae. If it is diatoms, they will eventually go away after all the silicates in the sand are gone.