TA/pH Condundrum

[Endless]

If I maintain the TA between 80-90 in our Endless Pool as recommended, my pH will increase every couple of days, rather than remain stable -- for example from 7.4 to 7.6 (regardless of swimming activity). However, if I let the TA decline between 40-50, the pH will remain stable for at least four days before it increases (pH of my water never decreases, only increases). Also, after I shock with CL-free shock, the pH will stay stable for up to 7 days. I maintain the pH between 7.2-7.6 and CL between 1-3 ppm.

So, anyone that may have an explanation as to why the pH fluctuates when the TA is at the recommended level, but does not fluctuate as frequently at the considerably lower level. I'm all ears.

Further -- is there any downside to the TA between 30-40 if the pH is between 7.2-7.6? (Our Endless Pool has stainless steel benches and swim-motor housing and there's been no rust or scaling over the past several years, even with TA is low, but pH within proper range.)

 

[newdude]

TA and PH are best buds joined at the hip. Or maybe TA is the old ball and chain and if it's higher, it pulls the PH up even faster and when it's lower, it's harder for the PH to rise like it wants to.

PH TA Relationship - Further Reading

www.troublefreepool.com

PH - Further Reading

www.troublefreepool.com

Your pool is telling you it wants the PH on the higher side of OK (any 7 is fine). Operate in the high 7s and only lower to 7.8. If you overshoot to 7.6 it will still be slower to bounce back than 7.2 or 7.4.

Your pool is also telling you that a lower TA thats still in range helps keep the PH in check. Run a 60 and it'll likely be much better.

after I shock with CL-free shock

Why are you shocking ? There's no need to shock in properly maintained water. It's an over correction, and MPS reads as CCs, further complicating things.

Pool Care Basics

 

[mgtfp]

It's all explained in the links that Newdude posted.

The main problem is that the pool industry only tells you half the story (either out of ignorance or because it's their business model).

This half is that TA is required as a buffer to prevent pH-fluctuations. So far so good. But what is actually the cause of "pH-fluctuations" that TA is supposed to prevent? Nothing really, unless you use acidic forms of chlorine (like trichlor tabs or dichlor shock).

What they don't tell you is that by adding baking soda to increase TA you over-carbonate the pool. Like soda water. And what happens to soda water when left open? The dissolved CO2 bubbles out, making the water taste less acidic - i.e. the pH increases.

The same happens in your pool (not quite as extreme of course, your pool water is not actually bubbly). The higher the TA, the more CO2 will outgas, the faster the pH-rise.

The industry-recommended TA-range is really only required when chlorinating with trichlor tabs. When using liquid chlorine or an SWG, then there is nothing that will pull down pH, and you will only see the CO2 outgassing effect.

That's why TFP recommends lower TA levels.

 

[newdude]

The industry-recommended TA-range is really only required when chlorinating with trichlor tabs.

And they don't even know why they say what they say, other than they say it. So when one changes the equation, with bleach and a mega spa / endless pool, they shrug and point to the paper that tells them the TA should be 120 and the PH 7.2.

See ???? It says so. Right there.


Anywho, listen to your pool, not the pool store. We'll guide you along the way.

 

[mgtfp]

Anywho, listen to your pool, not the pool store.

Well said.

This should be written down as TFP's Golden Rule. If there is one rule to be remembered - that's the one.

 

[Bperry]

If I maintain the TA between 80-90 in our Endless Pool as recommended, my pH will increase every couple of days, rather than remain stable -- for example from 7.4 to 7.6 (regardless of swimming activity). However, if I let the TA decline between 40-50, the pH will remain stable for at least four days before it increases (pH of my water never decreases, only increases). Also, after I shock with CL-free shock, the pH will stay stable for up to 7 days. I maintain the pH between 7.2-7.6 and CL between 1-3 ppm.

So, anyone that may have an explanation as to why the pH fluctuates when the TA is at the recommended level, but does not fluctuate as frequently at the considerably lower level. I'm all ears.

Further -- is there any downside to the TA between 30-40 if the pH is between 7.2-7.6? (Our Endless Pool has stainless steel benches and swim-motor housing and there's been no rust or scaling over the past several years, even with TA is low, but pH within proper range.)

Keeping your pH at 7.2 will make the pH rise faster as well. Let it go to 7.8 before adjusting it back down to 7.6.

 

[Endless]

OK, thanks all for the earful (in a good way) -- definitely gives me better understanding of the chemistry. I am wondering though whether the vinyl liner of the pool "likes" the pH to be lower than 7.8 with respect to prolonging its life span? By the way, always have used liquid bleach for chlorination.