Is it OK to close my pool with a vinyl liner with FC at 16.5 (CYA 40)?

[JaceTheAce]

Background

I live in Utah where we get cold snowy winters. This is the third year closing my pool so I'm becoming a pro at it. I'm meticulous about checking and balancing chems daily & weekly when the pool is in operation. In preparation for closing, 7 days ago I shocked using 7.5% bleach to raise FC to 16.5. In previous years over the course of the week the FC would slowly drop to a reasonable level by the time I closed the pool. This year, however, we had a cold snap and pool temps plummeted from 70's to 50's (Fahrenheit) and the chlorine level is not dropping. I tried forced aeration (using this method My $5 Return Jet Aerator) to off-gas to reduce chlorine levels and this has worked in the past but is not working this time.

Levels as of yesterday (10/27/2022):
FC: 16.5
pH: 7.7
TA: 60
CH: 300
CYA: 40
Temp: 54F

Questions
1) Will closing the pool with FC that high damage the vinyl liner or winter cover (thick winter tarp material)?
2) Should I consider using Sodium Thiosulfate to reduce chlorine in this case?

 

[Newdude]

SLAM level (40% of CYA) is 16 FC. It's perfect and safe for all finishes / equipment / swimmers.

54 is a bit chilly for me, but that's its own issue.

 

[JaceTheAce]

SLAM level (40% of CYA) is 16 FC. It's perfect and safe for all finishes / equipment / swimmers.

54 is a bit chilly for me, but that's its own issue.

Thanks for the fast reply! Good info. I probably won't worry too much about it then.

Yeah, 54F is chilly for me too but... I usually do a Polar Plunge with my teen boys the day we close the pool and of course they make jokes about shriveled raisins LOL. Being in-ground the pool doesn't freeze solid but by the time January hits it usually has a nice 1/2" layer of ice on the surface.

 

[Newdude]

I usually do a Polar Plunge with my teen boys the day we close the pool

Well you HAVE to have a last swim. It's in the rulebook.


We did the same. It was NEAT jumping in after lowering the water for blowing out the lines. Protip : no flips with the water lower. The extra hang time caused 1 1/4 flips making hard face plants.

 

[Newdude]

Good info. I probably won't worry too much about it then.

Also, remember this next year during the season. You have leeway above target range all the way up to SLAM, and almost none below target. Yet everyone tends to live in the yellow zone in between min and target, worried about having 'high FC'.

It does burn off quicker at higher levels, but most of it remains and I consider it a predose of the next day(s) loss.

 

[JaceTheAce]

Well you HAVE to have a last swim. It's in the rulebook.


We did the same. It was NEAT jumping in after lowering the water for blowing out the lines. Protip : no flips with the water lower. The extra hang time caused 1 1/4 flips making hard face plants.

NICE!

 

[Newdude]

NICE!

It was just as you'd imagine. An euphoric thrill followed by the record scratch freeze frame of realizing you were going to rotate too far, followed by a slow motion NOOOOOOOOOOOOOOOOOOOOOOOO

*SMACK*