First time winterizing

[JAFroese]

Started getting the pool ready for winter yesterday. Removed stairs, brushed and vacuumed. Water analysis was as follows:
FC 3.5
CC 0.5
PH 8.0
CH 25
TA 70
SALT 2130
CYA 50
Water temp 48 degrees F

My target for slamming was an FC of 20 (based on CYA OF 50). So I added 264 oz of 10.8% chlorine along with 4 oz muriatic acid to lower PH to 7.8 at 2:40 in the afternoon. There was a bit of sun on the pool for a few hours following so I retested at 7:40 in the evening. FC was 17 and PH still 8.0. I added additional chlorine to bring FC back up to 20, along with another 4 oz of acid. Tested this morning and FC still 17 and PH 8.0. Should I add more chlorine until it stays at 20??? The sun is rising and the pool will have another 8 hours or so of sun now. Or do I call it good and start draining and cover pool. And what about PH?

 

[Texas Splash]

The problem with your pH is that you are trying to test it while the FC is so high (over 10). We always recommend testing/adjusting pH when the FC is under 10. So if I were you, I'd hold-off on the bleach and let the FC come down so you can get an accurate pH check. It's possible it may actually be too low now after all the acid. Ooops. Confirm the pH, then bump that FC up to your SLAM and let it mix for 24 hours and you should be fine.

 

[JAFroese]

Oops. Didn't know that about PH and chlorine! Even with the 8 oz of muriatic acid though, it shouldn't have dropped the PH below 7.6... With the slam, do I need to wait until chlorine maintains a reading of 20 overnight, or is a 3 ppm loss considered acceptable?

 

[Texas Splash]

You really should not lose 3 ppm of FC overnight (no sun). If you are, there may be something brewing in the water (organic material). To check, you could raise your FC to SLAM/Shock level and do an OCLT. Check the FC at bed then again in the morning before the sun hits the water. You shouldn't lose more than 1ppm of FC. If you pass that, then just let that high SLAM FC mix for that 24 hours and you are good-to-go.

 

[phonedave]

Maybe it is bad advice, but I am never that picky at closing. I get my numbers right, and then dump in a lot of bleach so it goes to AROUND slam levels. I let the filter run for a few hours while I do a final vacuum and get the cover ready, and then I close it up. I don't see the need to get all fussy about 2 or 3 ppm of FC when the pool water is going to sit, unattended, for a couple of months at varying temps.

For the last three years I have done this, and have opened to clear water with a FC of about 1 to 2 ppm and CC of less than 0.5 ppm. A one day SLAM then sets everything right.

-dave