Water balancing, CYA, CSI, & LSI

[Stray-cat]

Bought a house with a pool about 2 years ago, finally made the decision to jettison our service company and do it ourselves to save the money. Took the summer to figure out the basics - cleaned the SWG, replaced the filters, have been procuring and adding chemicals as necessary to help bring some of the parameters in balance (brought FA down, CH up, added borates), and down to 2 that aren't per the official guidance that I want to ask further about to determine how important it really is to bring them inline.

This morning's measurements:

• FC: 6.5, no CC
• pH: 8.0
• TA: 70
• CH: 375
• Borates: ~45
• CYA: <30

My CSI calculates out to 0.06 in the poolmath app, and for grins I also downloaded the Orenda app and my LSI calculates out to 0.02. So, effectively perfect.

BUT - per the TFP recommended ranges, ideal pH is 7.6-7.8, and ideal CYA with a SWG is 70-80.

• pH: I've read that SWG's tend to incessantly drive pH up. When I was adding muriatic acid to bring TA down, my pH would go down as well of course, but would pop back up to the 8.0-8.2 range (from ~7.0-7.2) within a day or two. If I do nothing at all for a week, the pH just hangs out at 8.0-8.2. I don't want to keep adding muriatic acid all the time because I don't want to drive my TA too low and I don't see the point if pH is just going to pop up again fairly quickly, but then level out at about 8.2.
• CYA: TFP appears to recommend a much higher CYA for SWG pools than non-SWG. My house/pool is on a west-facing hillside with very tall trees to either side; the entire pool gets sun from ~10-7 in ~Jun-Jul, but this time of year only half the deep end gets sun from about 12-3 then maybe another 30 min before sunset, and by winter it effectively doesn't get any sun. The SWG is always generating chlorine (recently I've set it to ~10%), and chlorine doesn't appear to get consumed very quickly, especially this time of year (and the pool is now fairly chilly, so it's not getting used either).

How much do I really need to care that these two items are out of the recommended range, since my CSI/LSI look good?

On a side note, I plugged in the center of all the TFP ideal ranges for everything in the Orenda app, and it tells me that my LSI would be way out of balance. So that's interesting....

 

[PoolStored]

• pH: I've read that SWG's tend to incessantly drive pH up. When I was adding muriatic acid to bring TA down, my pH would go down as well of course, but would pop back up to the 8.0-8.2 range (from ~7.0-7.2) within a day or two. If I do nothing at all for a week, the pH just hangs out at 8.0-8.2. I don't want to keep adding muriatic acid all the time because I don't want to drive my TA too low and I don't see the point if pH is just going to pop up again fairly quickly, but then level out at about 8.2.

SWG is pH neutral. Let the pH hang out at 8.0. pH rise is highest when pH is low (like when you drive it down to 7.0/7.2) and when TA is high. You might lower your TA to 60, and pH will likely hang out around 7.8 - 8.0, which is just fine.

• CYA: TFP appears to recommend a much higher CYA for SWG pools than non-SWG. My house/pool is on a west-facing hillside with very tall trees to either side; the entire pool gets sun from ~10-7 in ~Jun-Jul, but this time of year only half the deep end gets sun from about 12-3 then maybe another 30 min before sunset, and by winter it effectively doesn't get any sun. The SWG is always generating chlorine (recently I've set it to ~10%), and chlorine doesn't appear to get consumed very quickly, especially this time of year (and the pool is now fairly chilly, so it's not getting used either).

High CYA is more important in the summer months. The basic reason for CYA higher is to reduce the amount of FC that the cell needs to produce, so it lengthens the life of the cell. No issue running lower, either summer or the startup/ending months. Just maintain your FC for your CYA...Link-->FC/CYA Levels

How much do I really need to care that these two items are out of the recommended range, since my CSI/LSI look good?

You don't.

 

[HermanTX]

First - thanks for using the PM app and following the recommended ranges.
It is difficult to try to run 2 different methods so stick with TFP and measure CSI with the app.
You should keep CSI slightly negative with a SWCG.

A SWCG is pH neutral. What you are seeing is a SWCG only makes chlorine whereas if you used pucks before, it contained both chlorine and acid, which help lower pH.

If you wish to run CYA at 60 with a SWCG, that is fine. If you pool does not have full sun then it will be just fine. just monitor it.

Try to lower TA to 60 and if it stays around 7.8 to 8.0 that may be fine.
Do you plan to keep your pool open through the winter? If so, you would want your pH in high 7's because the lower water temperature will drive down CSI.

 

[Stray-cat]

Thanks both. Can definitely drop TA further, and will of course keep an eye on FC & adjust the SWG output as necessary. I did purchase some stabilizer, just wasnt sure how critical it was to really start adding it. I'll probably just wait until next summer, and keep an eye on everything in the meantime.

I'm in GA; we haven't closed the pool prior years and I doubt the prior owners have either. I wouldn't know how to on my own, and don't think it's worth getting it professionally closed. I don't have a cover, so have to stay on top of keeping it clean of leaves and whatnot anyways. So it'll stay open all winter. If we really wanted to we could kick the heater on and keep using it, but that's generally not worth the expense! Wish we had a hot tub though....