What's your pH at now? It's not usually a good idea to mess with pH.
If it's for breeding fish, it's normally the hardness that's more important. You can mix your tapwater with RO (reverse osmosis) water to lower both your hardness and pH, but you will need to mix it at the same ratio at each water change.
In a dry climate, or when you have heating or air conditioning running, it's not unusual to lose a little water each day. Just top off with dechlorinated water, and it should be fine.