My thinking with the CO2 was that I've heard lots of suggestions that this brings the Ph down so it seemed like a beneficial measure. Are you saying that the side effects (lower oxygen, I imagine) would outweigh the benefits?
I don't have a practical alternative water source unfortunately (City living). I'd actually got to the point where I was considering an RO setup but I really don't want the extra hassle.
As Byron states above you can run tanks at almost any pH you like and the inhabitants will adjust. The problem with this is that when you go to add new fish to your tank it will give you a headache. That is why I say your fish tank should be kept very close to pH 7. This will allow you to add fish with very few problems.
You would think that would be the case. But in fact you most probably find that they will do what I did.If most of us acquire new fish from a local store, chances are they use the same tp water and probably do not do any adjustment re the pH. At least, my local stores do not. And as this pH is what occurs from my tap water, there should be no issues. If one is acquiring fish requiring a different pH, and has a tank prepared with such water, example an African rift lake cichlid tank with very hard and basic pH water, that is another matter. GH and pH buffering/adjustment would be a standard feature of such a tank.
You would think that would be the case. But in fact you most probably find that they will do what I did.
I would use natural neutral gravel for my acid loving fish, and a gravel that was Alkaline for my live bearers. We made sure that all the fish would be going into tanks with pH as close to optimum for that fish. Fish are transported across regions and countries, as a LFS this process is only possible if everyone keeps the fish in conditions as near perfect as they can.
In the situation above, this gives the LFS a problem. The person buys a perfectly healthy fish takes it home and it gets sick. Immediately the fish shop is to blame. Not the customer who has their tank set up outside of the range that fish would be expected to live in.