You have a helix dbs thermostat correct? You can use that thermostat on a glass tank. You sandwich the helix probe between the glass and uth and set it until the temp is no higher than 94 on the inside of tank on top of glass. If your only going to use the 20g tank to set the tub in then just put the uth on the tub with the thermostat probe sandwiched between and set so the inside of the tub under the substrate is no hotter than 94. Being your house is 77-82 that is perfect ambient for bps so you don't need to retain heat in anyways.

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