I recently began using a pressurized CO2 system that keeps my CO2 at 6.8 in
my 75 gal tank. My tap water is around 7.6 Ph and after several days of
aeration it remains at 7.6 Ph.

One day, I can foresee needing to do a large water change... possibly 50%
for whatever reason... I figure my fish would appreciate me avoiding
dangerously large Ph swings that would happen if I just dumped 35 gal of Ph
7.6 into my 6.8 tank.... I have a couple ideas:

1. Time: make the 50% water change last several hours, thereby buffering
the Ph spike.

2. Artificially lower the Ph of the new water with some type of acid
(Muriatic comes to mind)

3. Lower the Ph with an organic tannic acid such as peat.

4. Reduce my CO2 saturation by 50 percent and raise the Ph within the
operational tank before I do the massive water change.

5. There are probably another dozen ways to do this and I'm soliciting your
experience and ideas!

Do you have any other suggestions? What do some of you do to minimize the
Ph shock during large water changes?

Thanks,

DJay