Balancing chemistry before closing pool- Minnesota

[jmilhoan41]

Hi all- I have a question about balancing the chemistry of my pool before closing. This is the first summer I've owned the pool and the chemistry has been pretty stable up to 2 weeks ago, but the PH stayed at the lower end. I was primarily checking the FC, CYA and PH weekly with an occasional check of everything. Went on vacation 2 weeks ago; while gone it rained quite a bit and chlorine tabs ran out, so came back and tested yesterday- FC at 2.5, PH at 7.2 and CYA at 90. Some green spots in the pool from leaf debris, but not much. I got in yesterday (65 degrees) and brushed the pool, removed all the leaves and vacuumed. I used a calculator based on the CYA to get the FC up to shock level and added 4-121 oz jugs of 6% bleach per the calculations. Kept the pump on rest of yesterday and overnight and today checked all the chemistries (except the combined chlorine) and found this:

FC: 38 (was supposed to be at 36ppm for CYA at 90 per chart)
PH: greater than 8 (quite a jump in one day- not sure why)
Total Alk: Never did turn red- turned from green to clear and stayed clear forever and I stopped adding drops after 140 drops. I used 25ml pool water to calculate and on hindsight should have done the 10ml and used those calculations.
CYA: 100
Calcium hardness: 200

I just realized that I haven't been checking combined chlorine at all- so not sure if that was needed along with everything else.

I'm assuming I'll need to fix the Total Alk and PH before closing the pool, but I'm wondering if my adding algaecide before closing will affect either of those readings?

Secondly- I know that to balance my CYA I'll need to drain the pool and refill, which doesn't quite make sense to do before closing - drain 1/2, refill, then drain to 6" below skimmer. Will it hurt to leave the CYA alone and just refill in spring?

Thanks ahead of time for anyone's help

 

[JVTrain]

Your FC was higher than targeted because the pool volume you used was more than your actual volume, most likely. That's not very far off and should be fine.

Your pH is reading that high because the pH test is invalid and will read high at FC levels above 10 ppm. Trust your initial 7.2 reading before adding bleach.

For your TA test, see Extended Test Kit Directions The test will go from either green or blue, to red, pink or yellow at the endpoint. Repeat the test and your end point is when the color no longer changes, subtract the last drop that produces no color change.

No need to adjust anything. Even if your TA is high, that's a long term process to lower TA and can be addressed in the spring when you drain and refill to correct the high CYA. Next year, I would recommend switching to a manual bleach chlorination method to prevent your CYA from getting too high through the summer or upgrade to a SWCG system.

 

[Divin Dave]

Hi,

CYA - It sounds like you have a grip on what to do about the CYA. It wont hurt to wait til spring to correct that.

pH - If you tested pH AFTER the FC was raised, then that is a false test result. FC levels of > 10 will produce a high pH test. Always test pH with FC level below 10.

TA - if you tested TA with the high FC level, then what you describe as going from Green to Clear is most likely due to the extra high FC. Sometimes it's blue to yellow, depending on other factors. Here is a thread about a similar phenomenon. Strange TA test

CH - 200 is fine for a vinyl pool. Nothing needs to be done. I dont believe the high FC effects the CH test, but not 100% sure about that part.
I couldn't find any threads about high FC effecting the CH test.

 

[JVTrain]

Also, sounds like you have the beginnings of algae forming due to not enough FC for your high CYA. That may allow your FC to drop too low before spring but hopefully your water temp is low enough to avoid algae growth. It's recommended to close below 60 degrees and open before it goes above 60 degrees.

 

[jmilhoan41]

Thanks for the help- so very appreciated