Sand Lock up?
 

I have never touched my sand bed in my tank since starting it up, Today while cleaning the glass i noticed that the sand was hard about 1 cm down? Rock hard? The sand bed is about 3 inches thick. Has anyone else experienced this?

It is really the weirdest thing. I saw it last night. The first cm is fine but under that, it is like cement. You'd have to take a screwdriver to it to loosen it up.

Go to RC and search on "clumping" . Fairly popular topic with DSBs. Check Ron's forum in particular.