Here is an approximate guide to how hot your should be running your dip tank. Typically the higher you can run the temperature the better the shrinkage, however everything should be subject to trials to see the effect on your product.
Recommended Water Temperature
If your dip tank is switched off (and not heating), you shouldn't leave your dip tank with water in it for more than 12 hours. Water that sits in the dip tank for long periods can mark and rust around the waterline of the chamber.