F-U: Buffering for a higher pH

THanks everyone for your responses. I'll try my mest to get back to all of
you individually.

I've got a little more info to add:

This morning's tank readings:
pH: 6.2 (CO2's been off since Friday as an experiment)
Ammonia: 0
Nitrite: 0
Nitrate: 20-30 ppm
Hardness: 100ppm (I added a few shells to the filter box, in hopes of
raising the kH a bit.

I was thinking that If I changed my water source, I might help the situation.
Here's my tap water (B) compared to water from my Mom's (GR - one town
over, but a different system)

pH: B-7.0 GR -7.8
Hardness: B-80ppm GR-220ppm
B uses chlorine at 3-4 ppm, GR doesn't use chlorine or chloramine.
All other factors were zero (Amm, Nitrite, Nitrate)

Unfortunately, I still don't have a kH test kit.

I'm going to change about 5 gallons od the tank water with 5 gallons of the
GR water today, and see how it buffers over the next week. I'll add the
water slowly so as not to overly stress the fish (I'll use airline or
something small)

Thanks again, and let me knoe what you think of this plan.