Swimming Decorator crab

This prototype runs by a refrigerator timer motor and takes about 1 1/2 minutes for a complete revolution. I have noticed that rocks at low tide that are out of the water, but remain wet grow much more algae than rocks that stay submerged all the time. I am using that principal for this device to see if it grows more algae then my algae trough.
It is lit with 18 LEDs that are about 1/2" from the belt which is cotton cloth on a plastic screen which is simple to remove.
If it works ...

OK I have a theory and only a theory. As long as I have been keeping fish I am drawn to odd shaped fish like copperbands and long nose butterflies but I could never keep them as long as most other fish and looking back there were two causes for their deaths. One was jumping out. For some reason those types of fish like to jump. I lost about half of them from that. The rest of them died from something else. Last year I lost a copperband that got a bump and then a sore on it's side just before dying. ...