Can Polyquat raise pH???

[jeepers]

Very informative and makes sense, Chem_Geek. I didn't realize that the addition of the bleach would raise the pH and and assumed that I was OK to initiate the closing process at 7.6 without further adjustmemt. I falsely assumed that the polyquat was the culprit for the spike. And yes, your assumption of a CYA of 50 and jump of FC from 5.0 to 13.0 was right on.

All of this being said, how do you guys recommend that I proceed with the remaining step of covering the pool? Based on Chem_Geeks explanation I believe I understand that the pH would drop back down as the FC falls from the shock level. But will it continue to drop significantly and quickly enough once I add the light-blocking cover? If this were your pool, would you feel comfortable covering it up for the winter with FC of 13 and (based on CG's calculations) a current pH of 8.2? Or should I leave it uncovered for an additional day or two?

Jim

[chem geek]

I'd add one cup of full-strength Muriatic Acid (31.45% Hydrochloric Acid) per 10,000 gallons, let it mix thoroughly with the pump running (be sure to brush the area where you add the acid over a return flow) and after some hours, cover the pool and close it up. The acid will lower your pH to around 7.8 and as the chlorine drops slowly over time the pH might drop some, but not too much (even if all 13 ppm FC were to get consumed, the pH would not get lower than 7.2 and more likely won't get that low). If the water is cold, the chlorine should last quite a while. In my pool when covered and the water at 50ºF, my chlorine loss rate is less than 1 ppm FC per week.

[waterbear]

I would like to point out that even if the water test results are :
FC 15
pH 8.2
TA 80
CH 350
CYA 40
Temp 72 deg F (which is probably in the ball park, if not colder if you are closing)
then the saturation index is only .6 which, while at the upper limit of what is considered "in range" for a plaster pool and anything above that could be an indicator of scaling conditions, is still acceptable AND that the saturation index WILL continue to drop (move toward 0 as the temperature drops). IF the CH is lower than 350 then the saturation index will be even lower!
The high pH is really only a concern, IMHO, if you have very hard water or very high TA (or both). If your water is balanced to "normal" parameters it is pretty much a moot point and nothing to lose sleep over!
If you are normally dealing with very hard water or very high TA then you will know the associated problems and how to deal with them (or, at least, one would HOPE you do!)

As Ben said, high pH is not going to hurt anything per se, it just increases the probability of scaling conditions but the dropping temperature will lower the probability to scale by lowering the saturation index.

Just my 2 cents!

[CarlD]

What surprises me is that a quart of Polyquat didn't drive the FC to nearly 0. Usually it does, and I believe both 'Geek and 'Bear have explained why that is.

Carl

[jeepers]

Update, one week later.

FC 5.0
pH 7.3

Had the mesh cover on. I installed the solid cover today. Am I safe to consider this done for the winter?

Jim