Just an update on things.........I have had the new 170 gallon airpump running in the tank 24/7 for two days now. I still see a large pH swing (from 8.6 at dusk to 7.4 at dawn). Do you know if this is normal or should there be something else I do to help buffer this?

Most products on the market (like pH down) are only temporary things, so I really don't want to use those since I'm trying to tackle the root of the problem. During the day, the plants pull all the CO2 out of the water (driving the pH so high)......but at night, when photosynthesis isn't taking place, the CO2 drives the pH back down (to 7.4). I have read that fish should only experience a .4 to .8 change in pH.......and my swings are greater than that.

Hopefully it all balances out soon. I don't know if that's even the root of my problem, or if the problem has been fixed yet (as far as improved water quality)......but I will keep you all posted.