^^^ this is probably the best advice for a Glass tank, and Safe too.
With a 20 Gallon tank I’ve run a 100 Watt CHE without a Tstat in a house thats 68 at night and 70 day during winter and it kept the 20 Gallon breeder tank 78-80. This was only for a short Quarantine and I was home the entire time keeping a eye on it. The problem with not using a Tstat is that when the room temp changes the tank temp can sky rocket.. Thermostats will regulate that safely.
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