errant pH readings ?

[Cal_stir]

I run my skimmer air thru CO2 absorbant, my ph is 7.5 without it and 8.3 with it. My sump is under my basement stairs, I tried drawing outside air but didn't see any significant results.
I don't understand why people who don't test ph tell others not to, maybe there ph is ok and not testing it doesn't matter.
Everything I've ever read says that 7.5 ph is too low, my tap water is 7.6.
I monitor ph mainly as a quick indicator of chemistry problems and find it hard to believe that a ph of 7.5 is not detrimental to the long term health of a reef tank.