Cloud-9 is right on.
Lol, be careful though.... You don't want to put "methanol" in your tank--- methanol is the fuel that Big Foot, Grave Digger, and other monster-trucks and dragsters run off of--- makes gasoline look like cherry coke. "Methylene" is a different story....
I, personally (as well as most here I'd bet) wouldn't bother with the methyblue or melafix as a constant additive. Just dechlorinate the water with Prime or Amquel Plus (both of which remove ammonia from chloramine in tap water) and make sure it's the right temp (for bettas I've always done the finger dip, but ONLY b/c I've done it for years and know how much is too much). Long range exposure to methyblue *may* have degenerative effects on the fish. It's really a dye (as I'm sure you're boyfriends fingers are aware of) that just happens to be a good fungicide.
Melafix is made from an herb of some sort. A fantastic bacterial remedy. Useless, as far I I'm concerned, as a preventative. It stinks (smells worse than eucalyptus) and I bet the betta would call you dirty names for using it in his water if he could.