Closing chemistry recommendation

[SunnyOptimism]

So here's how I'm reading the info in this thread-

You bring you water to shock level to clear it.

You wait some amount of time and then add polyquat

You wait a little longer and then raise your FC again and close.

The problem I see is that, based on the manufacturers recommended process, if you follow the CYA/FC relationship (as you should) then your shock level of FC is definitely going to cleave the PQ into smaller subunits unless you wait long enough after shock level for the FC to drop below 10ppm. If you look carefully at what the manufacturer says, they say to shock up to 5-10ppm and then "wait a few days" before adding the PQ. That tells me that the PQ is definitely going to cleave.

I guess the ultimate question is, at what FC does PQ start to cleave into smaller fragments and at what FC is the PQ's algaestatic properties completely destroyed? That last part would set the upper bound of how much FC you can have in the water when you add the PQ. Add the PQ too soon after raising the FC to shock level and you risk the chlorine burning up all your PQ.

Interesting stuff here.....

[JimK]

So here's how I'm reading the info in this thread-

You bring you water to shock level to clear it.

You wait some amount of time and then add polyquat

You wait a little longer and then raise your FC again and close.

The problem I see is that, based on the manufacturers recommended process, if you follow the CYA/FC relationship (as you should) then your shock level of FC is definitely going to cleave the PQ into smaller subunits unless you wait long enough after shock level for the FC to drop below 10ppm. If you look carefully at what the manufacturer says, they say to shock up to 5-10ppm and then "wait a few days" before adding the PQ. That tells me that the PQ is definitely going to cleave.

I guess the ultimate question is, at what FC does PQ start to cleave into smaller fragments and at what FC is the PQ's algaestatic properties completely destroyed? That last part would set the upper bound of how much FC you can have in the water when you add the PQ. Add the PQ too soon after raising the FC to shock level and you risk the chlorine burning up all your PQ.

Interesting stuff here.....

I was wondering about that also.

[CarlD]

Not me. I've been using an effective method of closing for over a decade.

[amillionpets]

I've read this entire thread plus other helpful closing information on the site. THANK YOU!

My question: When you refer to raising the FC to shock level to close, at what point on the "Ben's Best Guess Guide to Swimming Pool Chlorine" are you shocking? There are two 'Shock' columns with very different Shock levels. Should we use the higher shock numbers for winter closing?

[CarlD]

No. Use the lower value, I believe the left of the 2 columns. I do not recommend you closing your pool until any algae bloom is clear. Then raise to the lower shock level.
If your CYA level is below 10, use 10 as your shock level
Below 30, use 12.
Below 60, use 15,
Below 100, use 20,
100 or above, use 25.

[FormerBromineUser]

Last I saw was that your CYA was around 40 but were thinking about raising it. Did you? The number on the far RIGHT of the chart are only for mustard algae; extreme cases.

[amillionpets]

Last I saw was that your CYA was around 40 but were thinking about raising it. Did you? The number on the far RIGHT of the chart are only for mustard algae; extreme cases.

My CYA did raise, but it wasn't necessarily intentional. I began using Dichlor from Sam's in lieu of bleach. My CYA kept raising. I went back to bleach once it reached 70. Didn't want it to get any higher. So it stands at 70 as of today. I had a hard time keeping my pH down this summer. ??? Anyway, it's good at 7.9 now. TA=80. CC=0. Water temp is 45*.

Thanks for letting me know what the high shock level is used for.

[chem geek]

For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases the Cyanuric Acid (CYA) by 9 ppm.

[amillionpets]

Yesterday 10:12 PMCarlD
Re: Closing chemistry recommendation

No. Use the lower value, I believe the left of the 2 columns. I do not recommend you closing your pool until any algae bloom is clear. Then raise to the lower shock level.
If your CYA level is below 10, use 10 as your shock level
Below 30, use 12.
Below 60, use 15,
Below 100, use 20,
100 or above, use 25.

Thank you, Carl. That's exactly what I needed. Leaves are still falling off of the trees here, and the temps are occasionally dipping below freezing at night. I'm not using a cover this winter. Too expensive just to have the wind rip it to shreds by the end of closing season. Nobody makes a cover that fits, or is meant to stay on, an AG vinyl sided Intex pool (that I can find) anyway.

I truly appreciate your quick response.