Chem_Geek is of course correct about what's going on, but here's a simplification and SLIGHT correction about what to do (sorry Richard ):

By keeping your pH at 7.2 or lower, the waterfall pushes the pH up. You add acid, pH and T/A come down, you run the waterfall, it pushes the pH up without pushing up the T/A as well.

So. I would suggest (and I RARELY do this) that rather than use Borax to raise your pH, you use Washing Soda (Sodium Carbonate). It's the same as "pH UP!" and other pool products that use soda ash to raise pH, but it costs FAR less. Arm&Hammer Washing Soda is usually next to the Borax in the detergent department. We don't usually recommend Soda Ash to raise pH PRECISELY because it raises T/A at the same time as it raises pH.

Alternatively, if you DO use Borax (and there's nothing wrong with that--I use it all the time) then you can equally boost your Total Alkalinity by adding ordinary baking soda (Sodium BIcarbonate).


It's cheaper to use washing soda because, pound for pound it's even cheaper than 20 Mule Team Borax--and you don't have to buy baking soda.

But either way is fine. The Borates, may, as Richard says, help your SWG run effectively at lower chlorine levels, so that may be a good way to go. After all, even if you use Borax and Baking Soda from the supermarket, it's still pretty cheap.

So:
1) NEVER let your pH go below 7.3 unless you WANT to lower T/A
2) Raise pH by adding either Soda Ash (washing soda) or Borax.
3) Raise T/A to over 100 but not over 125 by adding Soda Ash (which you did in 2) ) or adding baking soda.