Most water comes out of the tap at pH levels above a neutral 7.0. This is because municipalities are concerned about the long-term corrosive effects of acidic water so they adjust accordingly. If your system water comes from a well, you will probably discover the same thing, but in this case, it is the mineral content of the water that is keeping your pH high.
Good news – a slightly high pH is usually not a problem – here’s why. When you start up a new aquaponics system, you “cycle” it. The “Cycling” process is designed to encourage beneficial nitrifying bacteria to take up residence in your system. This process is entirely focused on the bacteria and the fish and, remember, they both prefer a higher pH. This means that water that is a bit above a pH of 7.0 actually helps to get your system “cycled”. Once the nitrogen cycle is fully established, and you have added plants to your system, you will usually see the pH of your system decrease over time. Why? Because the nitrogen cycle actually produces nitric acid which will naturally cause your pH to go down.
But there will be times, especially when your system is young, when you will need to act to push the pH down. And, conversely, over the long run you will regularly need to raise your pH.