So, we bought the Helix DBS1000 proportional thermostat to maintain the most stable possible temps. And it's working pretty well, but with one thing that's puzzling: When the temps are around 91.7-92.0 during the day, they go down as far as 88 degrees at night.

Here's the set-up:

Flexwatt taped with foil tape directly to the bottom of the tub, which is raised about an inch off the surface below. The thermostat probe goes through a little hole in the bottom of the tub and is wired securely against the bottom of the tub inside the warm-side hide. (Yes, I know, everyone says to put it outside the tub between the flexwatt and the tub, but I could *not* for the life of me convince Carey, so we compromised and wired it securely, with the cord leading through a hole in the bottom.)

The thermometer is an Accu-rite with the temp probe set under a thin layer of aspen substrate against the floor of the warm-side hide (held in place by the weight of the rather heavy hide).

The tub sits in a rather warm room of the house that gets very warm (84-86 on the warmest day) on sunny days due to south-facing windows. It can get down to around 75 degrees at night in the same room.

So temps in the room fluctuate quite a lot, but they do not get above 84-86 on the warmest winter day. I thought that the point of the thermostat is that it would compensate for the room temperature fluctuations. And it's not that the thermostat *can't* keep it warm enough at night, because we've tried raising the set temperature and can get the night-time temps up to 90 easily, but then the daytime temps top 93-94.

Am I missing something?

What's going on? And should I worry about it?

Thanks!

Heather