Can Polyquat raise pH???

I'm thinking that the answer is no, but here's my dilemma.

Closing the pool today. I'm handling the chemicals but have hired a pro to purge the lines. Two days ago I brought the FC up to shock level with bleach. Yesterday I added a little more bleach to maintain shock level and added a quart of Leslie Algae Control (Polyquat 60 equivalent). On Sunday when I started this process, my pH was 7.6. TA was a little low at 70 but has been 70-80 all year with a steady pH of 7.6-7.8 so I thought nothing of it.

In preparation for today's closing, I ran a quick FC and pH. FC was 13 (CYA 40) and pH was BRIGHT purple (>8.0). Keep in mind, all I've done since Sunday (when the pH was 7.6) was add several gallons of bleach and the bottle of polyquat equivalent. We have sprinkles today but no measurable rain.

I'm running the filter and added Dry Acid hoping to bring the pH down before the pool guy gets here and shuts down the filter.

Can the polyquat cause this? Can I close with a high pH? I'm leery to add too much more Dry Acid because I don't to have any areas of high concentration if it hasn't fully mixed before the filter gets winterized.

Agh. Up until now I felt like I was right on top of everything.

Jim

High pH is not as much of a problem with liner pool, as low pH, so don't freak out. If worse comes to worst, there's a way to add acid safely to a closed pool, and mix it adequately.

There's another report on the forum of this happening with polyquat, so it may be the polyquat + chlorine. But the truth is, I don't know. However, there is also a possibility that there's a testing problem, that the polyquat contributed to.

Do this:

#1 - Go to Walmart and get a gallon of DISTILLED (not: bottled, spring, crystal or anything but DISTILLED) water from their bottled water section.
#2 - Collect a water sample, and using a glass kitchen cup or something, mix up a 50:50 pool water : distilled water sample.
#3 - Test the pH of THAT sample, which will have 1/2 the FC or TC of your pool water, but virtually identical pH.
#4 - Tell us what you find.

Will do, Ben. Thanks.

In advance of my updated findings with the distilled water, can I still install the covers? (I have a mesh loop loc safety cover that I also then cover with a cheap solid winter cover). If I do need to add acid will I be able to safely do so with the cover on and/or partially in place?

Also, let me add this to the equation. So, as I reported my pH this morning was >8 (bright purple on the Taylor FAS-DPD). I cautiously added some dry acid and after circulating for about 1.5 hours had my pH down down to about 7.8 when the pool crew arrived. They got their signals crossed and added ANOTHER dose of algaecide. My pH is again bright purple >8 so unless I'm getting unequal distribution of the acid it would appear on the surface that there may be a correlation between the algaecide and my pH readings.

Does the double dose of algaecide raise any concerns? The pool crew laughed it off and said I won't have to wory about algae over the winter.
Jim

It's not the Polyquat, but rather the chlorine you added. When one adds a hypochlorite source of chlorine to the water, the pH rises. When the chlorine is used/consumed, it falls back down, but since you are adding it to shock the pool AND you are maintaining the high level, the pH stays high. Specifically, if I use your starting numbers of pH 7.6 and TA 70 and I assume you have CYA in the water (I assumed 50 ppm) and I assume you went from an FC of 5 ppm to 13 ppm, then the pH would rise to 8.2 from the addition of chlorine.

Also note that the pH test isn't accurate at high chlorine levels, but I would assume that your reading is in fact correct -- the pH is probably around 8.2 as predicted.

Ironically, having CYA in the water exacerbates this effect. CYA is an active chlorine (hypochlorous acid) buffer so as the pH changes it resists changes to active chlorine concentration. But this makes a large change in chlorine concentration result in a larger swing in pH. Basically, most of the hypochlorite you add combines with CYA and in the process this raises the pH (mostly OCl- + H2CY- ---> HClCY- + OH-). If there were no CYA in the water at all, then the pH would have risen only to 7.8 (less than half OCl- + H2O --> HOCl + OH-). In your case, the lower TA doesn't help either and I assume you have no borates in the pool.

This is why I usually recommend for people to lower the pH first before shocking. The main reason for this is to prevent metal staining that can occur from higher pH (scaling can occur as well, but only if the water is already fairly saturated with calcium carbonate -- that is, the saturation index is already >= 0). Otherwise, as Ben wrote, there isn't usually a problem from higher pH.

If you had initially lowered the pH to 7.4 before you started shocking, then the pH would have risen only to 7.8-7.9. If you had a TA of 100 instead of 70, the pH would have risen to 8.0 - 8.1 instead. If you had 50 ppm Borates in the pool, then the pH would have risen to only 7.8 (yet another great reason for having borates). For the masochists among you, you can calculate these things using my Pool Equations spreadsheet.

Ok.

I stand corrected. Thanks, Chem_Geek.

Ben

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

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.

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!

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

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