Tracy,
If you look back at the beginning of this thread, you should see the enclosure we made. It is insulated with R-13 and vapor barrier, We only loose about a half a degree a night with it. On sunny days we can add as much as five degrees back into the water. Our tricky spot is when it is cold and heavy overcast for days, then we loose a little at a time and have to wait for the sun to come out and "refill" our heat sink. So far 77F is as low as it has gotten. The fish seem happy and healthy and our water quality looks great.
