Want to close, but pH continues to rise / FC & Polyquat

[TonyMoc12549]

Good morning. I've had the pool covered and running 5 hours per day for the last month. While I have been waiting for the water to drop below 60 degrees in order to close the FC level has been really consistent...was going down about 0.5 every 3-4 days while the water was warmer. During the last month, the only number I've had issue with is the pH which seems to continue to rise and level off at about 7.6/7.8 at which point I bring it down to 7.4 which is where I believe I want to be for closing. Well, with the last few days cool weather (26 degrees this morning...so left pump running overnight) my water is at 55 degrees and I'd like to close this week.

My numbers are:
FC = 6.5
CYA = 30
pH = 7.6
TA = 100
CH = 400

Questions:
1) Do I just bring the pH down to a low 7.4-ish and call it a day and close?
2) I'm at 6.5 FC (about half of shock level) so once I take my water level down, I will add polyquat and continue to re-circulate for several hours. Do I check FC level again before closing and raise it above the 6/6.5?

Thanks all.
Tony

 

[Texas Splash]

Hello Tony. To help answer your questions:
1 - Adjust your pH to the recommended level of about 7.5.
2 - Your SLAM/shock level is an FC of 12, so do that after adjusting the pH and let is mix for 24 hours. Then let the FC drop back to your halfway mark (FC 6) before adding the Poly 60. Once the Poly 60 is added, let it mix for about an hour then drain/disconnect or perform any other closing procedures you need to.

Hope that helps.

 

[TonyMoc12549]

Pat, thanks, I'll do that...Poly 60 will be last chemical before i blow out the lines. I just don't understand why pH is rising this time of year...when generally all pool season it doesn't move. Thanks again, Tony

 

[chem geek]

The pH will naturally rise as the temperature gets lower, though it's not a huge change where going from 85ºF to 55ºF the pH would rise from 7.5 to 7.65 even with no carbon dioxide outgassing. This has to do with the temperature dependence on the chemical equilibria that affect pH.

At pH 7.4 there will be more carbon dioxide outgassing so that may also be part of the problem. I wouldn't worry about it and just let the temperature drop and then adjust the pH prior to closing.

 

[TonyMoc12549]

Thank you for the explanation. I'll adjust the pH, close and not worry about it until April. With the pool water at 55 degrees it's time to close! Thanks again!