the pH of my aquarium water is extremely high, on average it is around 8.7. It fluctuates between 8.6 in the morning before lights go on, and 8.8 before they the turned off. i am using Milwaukee 122 recently calibrated and have verified these reading using an API test kit. I know i should not to chase numbers, but this is extremely high. I started adding 60 ml of seltzer a day (10ml a time) to add co2. And was bring it down by no more then 0.1 a day (didn't want to shock the tank by bring it down faster). When I stopped, pH went right back up. I checked KH, it is at 2.7, do it shouldn't be causing high pH. I did a lot of research, and realized that pH of my tap water is 11. After it goes through RODI unit it becomes unmeasurable, but still shows 11. After I mix in the salt, it shows pH of 9, and let is sit for 12-24 hours, it still shows 9. Obviously when doing a wc the overall pH of my tank raises. I thought perhaps my RODI was leaving chemicals in the tap, so I ran KH tests and TDS both showed 0. I read that different municipalities have different pH readings and add chemicals to set it at a particular reading. I can't figure out what is added and how to neutralize it. And whether I need to treat my freshly made saltwater prior to adding it to the tank (perhaps with either adding vinegar or co2) to bring pH down to say, 8.6 and then by 0.1 lower each time a do a WC. Any thoughts?