I have that heater, sometimes it does weird things, but unplugging it for an hour fixes it. I've had mine for about a year and now I cannot change the temp setting, but that's ok.
Always get a heater a size bigger than what your tank is, you might need it one day for a freak cold spell or something.
As for water changer, I made my own, so can't help you with store bought stuff. Is that one of those where you have to have the faucet running for it to work? If so, that's a massive waste of water and if you pay for your water, your wallet might suffer later.