I have a spare 75W submersible penn plax heater and found something useful for it to do. My DIY CO2 doesn't react that fast in the winter since my house temp is about 62F and after putting the bottle in a bucket of warm water, result were amazing. Increased from 18 bubbles/min to 45 bpm. The bucket is 5 gallons, but I'm filling it with only 3 gallons of water. I want to keep the temperature at 72F.
By the 5W/gallon rule, a 75W heater should be used to heat 15 gallons, but I'm using it for 3. Plus there will be no circulation.
Simple question, are there problem using a heater in a volume of water far less than suggested plus w/o circulation?