I would suggest that with a heat source directly on a tub and given the cool room temp and the swing of a hydrofarms. It can produce very high temps in this case (very slow probe response with a slow software controlling it and a large swing 3º) In my tests I was able to produce spikes of over 100º inside the tub.

With this in mind I would not suggest a on/off t-stat for a single tub in a cool room. To prevent this you would need a proportional unit. My suggestion would be a herpstats intro.

You are still going to have issues with your cool end temp and ambient temps in a room that is 70º Most solve this by adding an oil filled heater to the room.

An alternative...
http://ball-pythons.net/forums/showt...arium-Solution