Can't raise pH into normal range

[wtoman]

I've tried lots of things, but I can't get my pH to rise into the normal 7.2-7.8 range. I have a manually chlorinated vinyl pool, 25K gallons. I test with a TF-100 kit. Current test is FC 4, CC 0.5, pH 7.0, TA 110, CH 350, CYA 30, Temp 84 degrees. This is a multi-season problem, no matter what I do, pH starts a slow steady decrease down to 6.8-7.0 range... Things I've tried:

- Raising pH with Borax. Works great, but then pH immediately starts to degrade back down to 6.8-7.0 range on its own. Repeatedly adding Borax eventually pushes my TA too high.
- Using un-stabilized chlorine (calhypo)
- Using a pond aerator whenever the cover is on

Probable contributing factors - I keep the pool covered to conserve heat, and I drain below the return lines for winter, meaning I usually need to add stabilizer each year - either as granules or with chlorine pucks. I am not adding stabilizer at the moment.

I can't seem to break out of the "pH low, TA high" pattern. The water is fine and perfectly swimable - if it weren't for the vexsome little pH test kit, I wouldn't know any different.

Looking for advice - I can't think of anything else to try.

 

[YippeeSkippy]

No pucks being used, right? Can you test your fill water for us, please? For a reference:

 

[Dan Morrill]

You are a ways off of having TA that is too high. Yes, you are in the upper (or Above) range that is industry recommended, but TA's only role in your pool is to control pH. The only side effect of having high TA is that your pH drifts upwards. Your pool isn't there yet.

My TA is 140, and barely creeps up during the season. In fact, at the start, I too struggle to get the pH up to 7.2 after opening from winter. I end up having to add muriatic acid once or twice a season, and that is it.

So two things: First you could try raising your TA even higher. Going into the 140 range would be totally reasonable I think in your case. With a higher TA, aerating should have more of an impact on your pool. Secondly, have you tried aerating with an air compressor? They make a lot of bubbles! Takes my pool a couple of days each spring (5-6 hour stretches each) to go from high 6's to 7.2 using a blower end held open on my air compressor. Then my pH very slowly drift up all season.

 

[wtoman]

No pucks being used at the moment. I fill naturally with rain/snow - so fill water is pretty pH neutral; and I don't have any on hand to test. (thankfully in the case of snow)

I have speculated that deliberately raising my TA higher than 120 might counteract my steady pH decrease, so it's nice to see that as a suggestion Dan. Between Borax, Baking Soda and Washing Soda I should be able to drag both pH and TA up, then see if higher TA + aeration can keep it stable... I am aerating with a small compressor meant for aerating a Koi pond - indeed it makes lots of bubbles. I've been very surprised to see no movement at all in pH despite having that aerator in place for weeks - it's part of why I'm so confused.

So my plan is now to push pH to 7.5ish, and TA to 140ish, keep aerating, and see how it goes. Open to other brilliant ideas from members out there if I'm missing something.