"dust" on my live rock

[Nanni]

There is what looks to be dust all over my live rock and even the plants in my 90 gal tank. I can clean it off, but it will be back by the next day. We've had the tank a few months now and this has only started happening within the last few weeks. There are also places where the previously colorful rock has started to lose it's color, and small places on the rock where it appears to have worn away. There was one rock that split in two and another has a new hole in it. Does anyone have any idea what could be causing this? Any help would be appreciated.

 

[ChrisRD]

What color is the "dust"?

BTW,

 

[Nanni]

The dust is grayish.

 

[Bojangles]

Did you or have to put in recently more/new sand and/or substrate? I had that problem...few waterchanges cleared it up.

 

[ThrillYa]

Do you have any urchins in your tank? Some species bore holes in rock and most eat the colorful coralline algae too.