For reference, I have posted in spas for my dad's octagonal orange hot tub here dad-s-spa-refilled-last-week-and-just-refilled-again-t35175.html
Dad refilled his 110+ CYA (in two weeks) spa today. The supply line is copper. Same as the whole house.
Kitchen tap PH is 8.0 which is what the water bureau intends it to be.
Test in the spa after about an 8-10 minute fill is 7.0 - It might be 6.9. I swear, I tested it within 15 minutes of starting the fill.
What the heck could cause this? Dad says the ph is always low. He's always raising it.
Now I figured the rain around here was lowering my ph. He has no rain. The spa is fully sheltered against all weather, although not entirely enclosed.