Greg Dalton wrote in message ...
Is it possible to get this pool acid from a pool store ? How about a friend
with a pool?

Perhaps, or buy it and give them the extra, I think it's pretty cheap.

If the rock foams does that mean its bad?

Means there's CaCO3 which is what will slowly raise the both the GH
and the KH if ground up into fine grains and you don't do many or
large water changes.
GH rising has little effect any most every plant and it's not fast
with CaCO3 rocks, abd the KH will also rise, but it can effect the CO2
readings by changing the pH you need reach to get the correct CO2
level.
But it's slow to dissolve and be added to the water with CaCO3. Large
weekly water changes should prevent most any problem with the rocks,
but if you have a very high porous gravel from CaCO3, as often are
used in Marine tanks then the KH/GH is added much faster(fine grain
aragonite gravels etc).

The other thing to consider, although the KH may rise and the needed
target pH will also rise, the amount of CO2 being added is still the
same and the plant's CO2 remain the same.
Folks often forget that part.
You can check a pH/KH/CO2 table to see how this works.

Folks can vary their KH's and see if the CO2 ppm mg/l stays the
same(or pretty close, there is some error in the measurements of pH
and KH).
Here's a table:

www.sfbaaps.com
Also www.thekrib.com
Regards,
Tom Barr