New here. Been running tanks for quite awhile. Have a 30 gal. running now for about 8 years and have been doing min. maintenance for the last 2. I now have time to get back into it. The problem I have is I can't get the Ph above 6.4. All params are good. There is 1 large goldfish who has been there for 4 years. Gravel is clean temp is 75. Magnum 350 filter running fine and clean with dual Bio wheels. Tap Ph is 7.0. Do water change and Ph is down within 30 mins. Any thoughts? Thanks.