Unusual closing guidance

[TimZ]

We've used our pool company for opening/closing since it was built in 2020. This year, the closing paperwork has new guidance for gunite pools. They say to raise CH to 600-800 ppm and lower pH to 6.5. I think what they're trying to do is to (1) make sure there is ample calcium so that there is no leaching out of the plaster over the winter and (2) make sure the pH spends as much time in the 7s as possible before rising to its natural ceiling. However, the 600-800 ppm CH and low pH lead to a pretty strongly negative CSI, and are outside of TFP recommended levels.

Has anybody heard of this approach? I don't want to be stuck with needing to do water replacement to lower CH next year, and am concerned about causing problems with too low of a pH even if for a short time. My inclination is to instead raise my CH to ~500 (it's low right now, 250) and just take the pH to low 7s.

 

[JamesW]

Ask them to explain why they recommend this.

What is their logic?

 

[duraleigh]

I agree with you except I would leave CH alone. It is a naturally rising parameter on it's own and 250 is not dangerously low.

 

[TimZ]

Evidently this came out of a class the pool company employees took with Orenda. They pointed me to an Orenda article called Proactive Pool Winterization. The article recommends raising both CH and TA to set up for maintaining a good LSI at lower water temperatures. That makes a certain amount of sense, although the pool company's CH recommended levels still seem too high and they don't mention TA. I'm also unclear how the very low pH recommendation plays in to it.

 

[JamesW]

They say to raise CH to 600-800 ppm

Orenda says 500 to 550 ppm, not 600 to 800.

They also say that the number is higher than you want in the summer.

So, what happens in the summer when the calcium is still at elevated levels?

It does not just disappear.

Do not be afraid to raise your calcium to something way higher than you would operate in the summer. 500 - 550 ppm+ is great!

Proactive Pool Winterization: How to Prevent Calcium Crystals

An LSI-based pool winterization strategy can prevent problems like winter dust and calcium crystals. Enzymes and phosphate removal keeps a pool cleaner too

blog.orendatech.com

 

[JamesW]

On the flip side, when the water warms up, don’t freak out about super high LSI with 80ºF water, because

1. the pool was most likely diluted by rain and snow over the winter,
2. if it wasn't, the pool is about to be diluted when we refill the pool in the spring, and
3. water will not go from the 30ºs to the 80ºs overnight. We have time to ease out of winterization just like we eased into it.

They assume that there will be a lot of dilution, which is not always the case.

 

[SoDel]

I took the Orenda course and the advice your pool folks gave you isn’t anything I remember. My recollection is, adjust your pool chemistry so LSI remains balanced at both closing temps and at winter temps (freezing is assumed, ymmv). Use calcium instead of high levels of TA so pH ceiling is not bonkers high. Prior to closing, let pH float towards its ceiling and it will stay close to there over winter.

An example: closing temp is 65, winter low temp is 32 or thereabouts for the water.
pH 8.0
TA 60
CH 500
CYA 60
Salt 3000

At 65F, LSI = 0, pH ceiling = 8.01
At 32F, LSI = -0.27, pH ceiling = 8.07

Lower pH at closing will require more calcium, but I prefer the above because my pH does tend to rise over the winter despite the pool being covered, so I let it drift to its ceiling and then have it closed.