Finally tracked down why my pH kept creeping up every week

Started by Marcus Reed · · 3 replies
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#1
Small one but felt good. Every Sunday my pH was reading 7.8 to 7.9 no matter how much acid I dumped in Wednesday, TA sitting fine at 80. Took me way too long to connect it to my spillover spa jets running 45 minutes a day, basically an aeration fountain agitating water and offgassing CO2 nonstop. Cut that runtime to 15 minutes and moved it to right after my acid dose instead of throughout the day, pH has held at 7.6 for two weeks straight now. Should have caught this with the affinity laws staring at me the whole time, more surface agitation just means more CO2 loss and higher pH, it is not complicated once you see it. Anyway if your pH drifts up despite good TA, check anything aerating the water before you blame your acid dosing.

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#2
This is such a good catch Marcus, the aeration thing never even crosses your mind until you see it laid out like that. The one thing id add is my salt system waterfall does the same thing on a smaller scale, took me a season to notice pH crept up on the days I ran it longer for the kids swimming under it. Now I just dose acid a little heavier if we're doing a waterfall day instead of fighting it constantly.
#3
Spillover spas are basically pH strippers, glad you found it. Mine's the same setup, attached spa, and I noticed the exact same climb on the days the kids wanted the jets running for an hour instead of twenty minutes.

Now I just run it right before I'm already planning to add acid instead of treating it like a separate problem. TA at 80 means you've got room to work with, that's probably why you're not chasing your tail on top of the aeration issue, low TA and high agitation together would be a nightmare.
#4
Marcus, that's a textbook case and the affinity laws line made me grin, you don't see many people connect pump curves to pH drift. CO2 outgassing is really the whole ballgame here, carbonic acid leaving the water is what pushes pH up, acid dosing is just fighting a losing battle if the gas exchange rate stays high.

Karen's point about TA at 80 giving you room is right too, at TA 80 your pH bounce per acid dose is smaller so you were probably masking the aeration problem for weeks without realizing it. If your TA had been up around 110 or so the swings would've been nasty enough to chase down a lot sooner.