brown growth

Question
We have a saltwater tank with 3 fish and a spider crab.  Just today I noticed that the spider crab has this fuzzy brown stuff all over him...and this same fuzzy brown stuff is all on the inside of the tank.  We just cleaned the tank a couple of days ago.  Now the spider didn't eat tonight and is barly moving.  I'm not too sure what to do.  Any suggestions?

Answer
I am trying to figure out why the spider didn't eat the brown stuff does scare me, it is just probably algae. If you are having problems with algae test for phosphates. Do you use R/O water? What are you feeding the spider? Maybe try something a little more appealing like a small piece of shrimp.