Your heat tape should be set at whatever temp is needed to achive the desired hot spot and ambient temps in your tubs.

For example, I use a cool side temp of 82-84 degrees and a hot spot of 92-94 degrees with an open air rack system. The ambient temps in my facility run from 82 to 84 degrees and my heat tapes are generally set at either 95 or 92 depending on the size of the tub in the rack. Thermostats are a great help in regulating all of these temperatures.

The temp that you need to set "your" heat tape will really depend on the type of rack, size of tub, size of heat tape, ambient room temps, substrate, etc ... when I get new racks in it generally takes me 24 - 48 hours of "tweaking" the thermostats before getting it just right.

Hope this helps.

-adam