Well I tried adding a drop of the Alk #1 before the 5 drops of phenol red and now the Taylor kit reads the same as my other 2 el cheapo test kits. Without the Alk# 1 it still reads about .3 lower. Sooo... either the Taylor kit reads low and the cheap kits are right, or the Taylor kit already has sodium thiosulfate and adding a drop of the Alk #1 is doubling it up and causing a false high pH reading. If this is the case, the cheap kits are also giving high readings.

I think for now I'm going to trust the Taylor kit, but err on the side of caution and add muriatic acid whenever the pH reaches 7.5. I'll just be adding smaller amounts a little more frequently. This is probably better anyway since it will keep the pH from swinging much, and keeping it low (7.2 - 7.3) should help the SWG anyway. Even if it turns out the Taylor pH really does read low, the worst I'll be doing is keeping it around 7.5 - 7.6 which still isn't too bad, right?