dead fish?

[Namnuta]

You probably have a crab, and the head you saw was probably a molt. I have a crap in my tank that just showed up. I used to see him only a night, he would just come to the edge of his hole. Now he roams the tank and i see him every time i feed. Mine has spoon like claws and doesn't seem interested in my livestock at all.

Your cleaner could also be molting, as mine will disappear once in a while ( i assume to hide to allow his new shell to harden). If you see what looks like a cleaner body don't fret right away, becasue is could and probably is just his old shell. When mine molts it old shell look exactly like him, legs, antenna and all.

[Madreefer]

If you want to catch that crab. Get a tall drinking glass and put some food in the bottom and place the glass at an angle in your tank. Preferrably when the lights turn off.