Lacking either a Zone VI compensating timer or a Haas Intellifaucet I tried the 'ol fishtank heater trick. I worked great! I'm lucky in that my darkroom is in the basement with a separate zone. I keep the thermostat at 68, and keep 3 gallon jugs of water so to start all my chemistry is 68 degrees. It usually drifts down, from evaporation, I suppose. The submersible heater kept the developer temp constant, while the stop, fixer, etc drifted down to 66, no big deal.
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