I'm at my wits end trying to get the ph and TA in my 300gallon spa in check. Granted as the name illustrates I'm quite green to all this but something just isn't adding up. All measurements done with a new k-2006 kit. Spa has been drained many times over, followed the decontamination process (spa flush, drain, refill, 1/4 gallon 6% bleach, drain, refill).
Out of the tap the CH was 50 - I added enough calcium to get to 110-120ish ppm. TA is now 50, ph 8+ (scale on 2006 only goes to 8.0, both numbers the same directly from the tap before spa was filled as well). I added Alkalinity Up (discovered too late that its just baking soda after I bought it... next time) to reach 80ppm. Added dry acid to bring ph back down and now TA dropped more then expected, 50. I keep going back and forth between the baking soda and dry acid, just seems they are moving TA and PH way more then expected. Who knows how many ounces of product's in it now.
Latest iteration - ph was at 7.2 and alkalinity at 30ppm. I added one ounce baking soda (I'm using measuring spoons, no accurate scale available). Per the calculator this adds 15 ppm TA, which tests confirmed. But instead of ph going up by 0.03 per the calculator it went up by 0.3, now at 7.6 maybe 7.7 even. What gives? I know aerating from the jets raises ph, but that much in maybe an hour?
Not sure how I'm ever supposed to come to a predictable balance. The same is true for ph. The acid demand test (similar results just using the pool calculator) said to add 0.4oz volume to lower ph from 8 to 7.5. It took way more then that to do it, maybe 3 oz to do it, which starts the vicious cycle again sending TA plummeting down. Argh. Heeeeeeeeeeelp....