Stabilizing my PH to 7.0

I have a 220gallon tank that has been setup for about a year now. I do 50 - 60% water changes every 2 weeks and I have always naturally kept a PH right about 7.0, maybe a little higher. My water comes out of the tap at about 8.0 but within a few days of my water changes the tank always ended up with a PH of about 7.0. This has worked fine for me.

Over the last few months I have added a lot of driftwood to my tank, and I now find my PH at 6.0 and even lower (very acidic). I have started using the seachem 7.0 neutral powder to raise my PH but it seems to be very difficult to maintain my PH even using this powder. The bottle says to add it once or twice a month, but it seems like I need to add it at least every two days to keep my water at 7.0. Any ideas on what I can do as an alternative to dumping seachem neutral powder in my tank every two days? It is becoming very expensive. Would my fish be okay living in 6.0 water? I've listed my tank inhabitants below.

Water Parameters Nitrate 10PPM, Nitrite 0, Ammonia 0, PH 6.0 (maybe even lower, my chart only measures down to 6.0)

Green Severum
Firemouth
Keyhole
Convict
1 bala shark
6 clown loaches
5 giant danios
4 australian rainbow fish
1 pleco
2 corys