I have had the same 40w fluorescent light over my 75 gallon tank for the past 2 months. Most of the crabs enjoy sitting on the cork bark way up high under the light. In the last 3 days, I added some additional "second levels" so they could have more room to bask under the light if they wanted to without all having to cram onto the same pieces of bark. Well, they have been climbing directly up into the ballast (housing) of the light and stay parked there for the entire day. I would understand if the tank were cold, but it is at a steady 75 degrees...what in the world are they doing? Any ideas?