To confirm-
Slam level fc for a cya of 40 is 16ppm
FC/CYA Levels
Going higher than that just wastes chlorine & risks damage to people, equipment & surfaces.
For closing you want the water temp to be 60 degrees & falling. For me this usually happens around Halloween, sometimes a tad later.
Since I have a swg my cya level is generally around 70 or 80 so my slam level is either 28 or 31 at closing.
I clean the pool (the robot does), raise to slam level, do an
Overnight Chlorine Loss Test to ensure I am algae free, then close it up, I have a solid tarp style cover. I also keep my cover pumped off so I can easily peel it back a little if I need to peek.
I check fc throughout the off season (usually around Christmas & again in February) but I have never had to add fc. This year @ my February check I had 19ppm fc. We have had a warm March my fc is now down to 10ppm. So it’s time to get going!
With the cover on blocking the light & the water temp well below 60 degrees fc lasts a long time if you have no algae to begin with.
Most of my fc is usually lost between closing & the Christmas check likely due to the fact that higher fc levels deplete faster and more temp fluctuations during that time in my area. We’ve had 80 degree Christmas in the past- you just never know!
The later you can close the better.
The earlier you can open the better.
I personally like to do what I call “soft” closing & opening where I put the cover on before the leaves really start dropping & it’s too cold to swim but I am still running the pool as the water temp is right at 60 but the ambient temp is still fluctuating a bit. I can easily peel back the cover & add liquid chlorine/run my swg or throw my robot in etc. then a week or two later I fully raise to slam, lower the water & button every thing up before the risk of freezing.
At opening I repeat the process in reverse, I hook up the plumbing, raise the water, & get everything going, add salt to get the swg going etc (i am doing this now). Then in a week or so I will remove the cover after the majority of the dangly things & pods have fallen. I hate fighting with the debris daily when it’s too cold to enjoy the pool!
How ever you choose do it all the bases need to be covered:
*Water Temp 60 or below & falling
*Raise to Slam level for your cya
FC/CYA Levels
*ensure you’re clean & algae free with
Overnight Chlorine Loss Test
* check fc levels periodically during the offseason & replenish if necessary especially if the ambient temp has fluctuated a bit (it’s worth 5 minutes of your time in the off season to ensure you don’t open to a swamp)