How to keep sand white/clean????

So far I am really pleased with how things are going in my new 75 gallon system, with 1 exception.

The sand quickly starts to turn brown and the developes into a mat type of consistency on top.

I vac it once/ week when I do a water change, but it quickly re-appears.

Is their a good fix for this?

Sand sifting goby?, Cucumber?

 

Probably Diatoms. My tank had them as well. Over time they subsided and now my sand is free of the mat (It lasted about a month), The sand was slightly stained and never regained the bright white sugar look, it is more of a beige or light tan now. I added a fighting conch and 12 nassarus(sp) snails to fix it, but I think time is what actually did the trick.
I do like the fighting conch and nassarus snails for scavenging the sand bed though.

 

UV Sterilizer really helps and so does blasting the sand with a turkey baster to rotate it. Sand dwelling clean up crew would help minimally. The brown algae will eventually go away on it's own though as long as the water is right. Your tank is just getting cycled - that's a good thing even if it's not pretty. Chemi clean does take care of that, but I don't like using chemicals in my tank.