Big drop in TA, big spike in CH...I'm confused

[JamesW]

Maybe turn off the autofill for a few days to see how much evaporation happens.

In my opinion, all of the increase probably cannot be attributed to evaporation.

I would suggest that you maintain the CSI between -0.3 and 0.0.

 

[steveinaz]

Joyfulnoise;

Sierra Vista.
I was wondering what role The Natural Chemistry Scale Free might have. I was a little skeptical, but it has worked extremely well. No waterline calcium build-up, and my Salt cell was completely clean after coming out of system this fall. Even my waterfall rock has no calcium line, which you, as a Tucsonan, know is a miracle in itself.

 

[JamesW]

Using a CH of 325 puts the CSI at -1.0, which is very aggressive. Even at 825 calcium, the CSI is -0.61, which is still very aggressive.

With the CSI that low, you won't get scale, with or without a sequestrant.

 

[steveinaz]

The chart says the Target CSI is -.6; mine is -.61

At any rate, I'm gonna fix the problem, not the symptom, and do a drain as necessary to get me at around 400 CH. And COVER MY POOL...LOL.

 

[JoyfulNoise]

The chart says the Target CSI is -.6; mine is -.61

At any rate, I'm gonna fix the problem, not the symptom, and do a drain as necessary to get me at around 400 CH. And COVER MY POOL...LOL.

Install a whole house water softener with a run out to your autofill. I did it last May and my CH has gone down from a high of 1500ppm to 1100ppm now. Honestly, it should be illegal to build homes in Arizona without a main plumbing loop for a water softener hook up. The savings alone from damaged plumbing fixtures and reduced hot water heater life is enough to justify the installation.

You can’t keep a cover on much past June 1st here or else your pool water will boil. I left one on my pool until mid June a few years back and the pool water was up at 98F....too hot. Best to just manage your CH, TA and pH so that your CSI is always slightly negative (staying around -0.1 isn’t too hard). That will definitely keep scale at bay.

 

[steveinaz]

We do have a softener loop...hmmmm. Thanks for the suggestions. Any suggestions on a good softener?

 

[AUSpool]

Do you have an auto drain? If you do, check that there as enough gap between the auto drain and auto fill to ensure your not draining and filling at the same time.

 

[JoyfulNoise]

We do have a softener loop...hmmmm. Thanks for the suggestions. Any suggestions on a good softener?

Sent you a Private Message with details. There’s also a link in my signature detailing my softener installation.

 

[steveinaz]

Do you have an auto drain? If you do, check that there as enough gap between the auto drain and auto fill to ensure your not draining and filling at the same time.

No auto drain.

 

[steveinaz]

Here's my fill water chemistry:
pH 7.4
CH 160ppm
TA 180ppm
FC 0
SA 0

 

[JamesW]

What chart says to target a CSI of -0.6?

Yours has been between -1.0 and -0.6. That's too aggressive and will dissolve the plaster.

If your fill TA is 180, then you're adding way too much acid for it to be down to 50.

 

[steveinaz]

Sent you a Private Message with details. There’s also a link in my signature detailing my softener installation.

Thank you, you know my calcium pain. LOL We are going to do a water softener.

 

[steveinaz]

What chart says to target a CSI of -0.6?

Yours has been between -1.0 and -0.6. That's too aggressive and will dissolve the plaster.

If your fill TA is 180, then you're adding way too much acid for it to be down to 50.

I'll let pH drift up farther this week...but I don't get it, the 12oz each Saturday keeps it right at 7.4.

 

[JamesW]

7.4 is too low. I would keep it about 7.8 or 7.9.

 

[steveinaz]

Ok. Too weird I struggled in the past to beat down TA, and now I'm down to 50, and don't know how I got there??

 

[JamesW]

Every time that you add acid to lower the pH, the TA will go down as well.

That's why you should not lower the pH below 7.8.

In my opinion, evaporation can only explain part of the calcium hardness increase. I think that some came from the plaster.

With a CH of 160, you would need to lose 3 times the volume of the pool to get an increase of 500 ppm.

 

[steveinaz]

Agree, last year the pool was brand new, and it's first fill.

 

[duraleigh]

3/8" daily evaporation is plausible in that high Arizona desert. That a little over 11 feet annually....almost 3 times the volume of the pool.

 

[mknauss]

3/8" daily evaporation is plausible in that high Arizona desert. That a little over 11 feet annually....almost 3 times the volume of the pool.

True. But the evap rate does slow a bit in the winter. And at a higher elevation that the OP is at the summertime pool water temperatures are no doubt lower and thus less evaporation occurs at night compared to mine. We see ~88F water in the summer.

 

[JoyfulNoise]

Evaporation in Nogales (similar latitude but slightly lower elevation than Sierra Vista) is around 94" per year, not much different than Tucson, with more than 2/3rds of that evaporation happening between May & Oct. So while evaporation rates are high, they can't account for that much of a rise in CH.

I agree with @JamesW 's initial assessment - high evaporation + aggressive water removing calcium from the plaster surface. In a 13,000 gallon pool, an additional 250ppm of CH represents 27 lbs of calcium added to the water. Over a large surface area, that's probably not much more than a millimeter or two of material loss which would be practically unnoticeable to the human eye. The loss would also be distributed over the entire plaster surface and would be uniform enough to not cause any noticeable surface variations.

The prescription is easy - set the pH target higher (no lower than 7.6) and make sure the CSI remains closer to balanced (zero) or slightly negative (-0.1) so that the plaster is no longer affected and, long term, add a water softener to the house so that the fill water is calcium free. People that add water softeners to their pool's autofill eliminate most, if not all, of the CH rise that is typical around these parts. If a pool does not have softened water supplied to it, then the best you can hope for around here is to get 4-5 years on a fresh fill before significant draining and refilling needs to happen. It's just the nature of the beast in these parts ....