Did you let the tap water sit overnight to gas out before you tested it? Put some in a cup or bucket overnight, with an air stone if you have one, so the buffers and softeners and other chemicals the water plant adds to evaporate out and let the water reach the pH it will be in your tank. Then test. He could be reacting to the high pH. If your grocery store carries RO water, get a few gallons and use it for your next pwc. Many stores have a machine in the front where you can buy it by the gallon and fill up the jugs yourself. Distilled water is an option as well if RO isn't available. Many LFS's offer RO or RO/DI water by the gallon as well. It lacks minerals and buffers and is a healthier way to reduce pH than adding buffers. I would do a normal 50% water change and replace maybe 5 gallons of the fill up water with RO the first day, and then do smaller 10-15% changes every day after that with RO until you can bring the pH down to around 7-7.5 and see if his condition improves. If it does, just keep using it for your water changes. You may want to look into saving up for your own RO unit if it does help, it will be cheaper in the long run. You can usually find prime on amazon or eBay at great prices, and it really is the best out there.
