Help: Clumping Sand Bed

[PoonTang]

In the last 2 weeks or so I have noticed that my sand bed is starting to form large soft clumps and turning a slight grey colour. Its not Cal/Alk binding as the clumps are definately soft and easy to break up. My best guess is some kind of a bacterial bloom??? What, if anything should be done and what causes it. Any help would be greatly appreciated.Here is a bad picture of it.