Hot Tub water

We moved into our new house and used our whirlpool tub for the first time. Guess what, we ran out of hot water.We told the builder about the problem and he had a plumber install a 40 gallon electric hot water heater to the output my 48 gallon gas water heater (builder pick up the cost). I now get 120 degree hot water into my AKER 100 gallon whirlpool tube (average operational volume 74 gallon). My question is: 1 If I use the tub about every 5 weeks and I turn it on a day before will there be a problem with bacterial in the water from the electric tank? 2 Will the electric hot water heater cost a lot to operate If I leave it on all the time? I have a by-pass valves to both units. There are only two people living in the house that require hot water. Any advise? Thanks
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Depending on where you live the electric will use double of what a gas unit does. Sure it will cost to heat, wait for your bill. A larger gas tank would have been better, or gas tankless.
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Try one of these:
www.tubgirl.com
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