My pH at the tap is 7.2. My pH in the aquarium is 8.6. I did a water change 50% and my poH is now at 8.0. I would like to bring my pH a little lower. Do I keep doing water changes once a week to do this or is there some other way.? I've tried that "pH down" stuff but I find that I have to add allot of it just to bring it down 0.2 on the pH scale. Thanks.