What chemistry before closing inground pool

bostonpool

Well-known member
May 29, 2017
79
Worcester, MA
Hi folks:

Well my 32,000 gallon Gunite pool is closing tomorrow. Pool store coming out to help (I still am hesitant to do it myself.)

I've tried to follow the advice on here on what to do pre closing.

My question is around CSI. The info on this site says I should have PH between 7.4 - 7.6 and CH and TA "not too far out of line".

My PH is about 7.7, CH is 375, TA is about 75, CYA of 80, salt of 3000. Temp is about 70 deg, so CSI is about -0.24

But if I change the water temp on Pool math to 40ish, CSI goes down a lot to -0.53.

I can keep CSI more in check if I raise PH.

What do you guys recommend. Keep things where they are or raise it? I worry about CSI getting too negative over the winter.
 

anthonypool89

Well-known member
Aug 26, 2016
216
Berks County, PA
I'm no expert here by any means, but have been closing my own pool for 30 years. What I do is partially remove the cover during the off-season, agitate the water as best as I can (a kayak paddle works great!), then recheck the CSI. As I mentioned in another thread, I typically find I have to add pH increaser to bring it up closer to 8 as the water gets around the 45-55 range. Sounds like you're fine for now on the pH - since I also try to close the pool with the pH around 7.7, but, you're right in that as the temps drop, your CSI goes into the scaling zone. I know I try to micromanage this way too much cause, as was just pointed out to me, it takes months to form scale, so monitoring every few weeks or so, as I do (well, until the pool freezes anyway) is likely excessive. Others with far more TFP experience might differ, but I'd say to leave the pH where it is for now.

Just checked and I don't come up with the same readings you get on the CSI - I get closer to zero but I do mine differently being that I don't have any CYA, so I just use Temp, TA, pH, and CH to determine SI. Not sure I'd want to close in the negative zone however. If it were me, I'd try to get closer to zero. I see the TFP recommendation is 70-90 for TA, but I tend to keep mine around 100-110. Quite honestly, before I had the new plaster put in 5 years ago, I used to add the recommended closing chemical amounts, cover it up, and done until spring. But with the new plaster I'm admittedly a bit more paranoid about developing either scale or etching over the winter, so for me, there's some peace of mind in checking it every few weeks and adjusting pH if necessary.
 
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anthonypool89

Well-known member
Aug 26, 2016
216
Berks County, PA
bostonpool.....amazed to see that you have the old Apollo vertical filter! Me too! Mine is VA-52. I swear that, while there are disadvantages to these filters - such as not being able to vacuum to waste and lack of "multi-port" settings, these things are the pool equivalent of the old Kohler Cub Cadet engines - nearly bulletproof and just keep going and going. My pool went in summer of '89 and still using the original filter.

So far, how do you like the SWG? I ask being that I've already considered this. I started with chlorine, then switched to Baquacil about probably 20+ years ago or so.
 

bostonpool

Well-known member
May 29, 2017
79
Worcester, MA
Love the SWG! Granted this is my first pool and we added the SWG, so I have nothing else to reference. My Apollo is great. Only small issues like it tends to corrode a bit with the salt.

Thanks for the tips. Note I assume I have Borates of 15 and that changes some of the pool math calculations. I've never added borates but I've tested with a test strip and that is what comes up. Approximately.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
10,536
Northern NJ
...you're right in that as the temps drop, your CSI goes into the scaling zone.
CSI above 0.3 is the scaling zone.
CSI below -0.3 is the etching zone.

As temp drops your CSI goes more negative creating aggressive water that can erode plaster.

You keep your CSI slightly negative, between 0 and -0.3, to stay out of the positive scaling zone.