It's usually not a huge deal, although below 5.9 or so some bacterial processes like denitrification can be slowed down. There are a lot of people here that run mid 5's with co2 on because of low KH. I suspect that is your issue. with a tap of 7.2 you probably have driftwood or some other source of acid leaching into your water. Doing a 50% water change weekly will help keep the pH up with the same amount of co2 (usually).