Your adjustments sound good! Keep us informed! You don't really need to buy special water for him, though. If you get milk by the gallon or anything in a gallon (or even half-gallon) jug, just fill it with water and leave the top open. After a few days, it'll be totally safe for your snake to drink. It'll save you a little money, too! But he should also be okay drinking tap water, so long as there isn't something really nasty like alkali metals in your water which not even people should drink (can be a problem where I'm from if you don't live near a town). If that's the case, distilled water from the grocery story is pretty dang cheap. Probably much cheaper than anything Petco has to offer. I'm guessing the Reptisafe is just distilled water or even municipal tap water marked up to make the store more money.