chlorine dissipation - flat quantity or rate?

[jenrussell118]

Longtime listener, first time caller here.

Going out of town on vacation for 1.5 weeks and trying to figure out how often to have someone check in on the pool, and whether to bother having them check the FC or just add chlorine. Specs:
Above ground
24' round
14,500 gallons
82-85 F
CYA: 40
pH: 7.5
TA: 75
(Yes, I use Taylor reagents for all testing! And the premium Pool Math Android app for tracking )

Pretty much the only treatment it needs is regular doses of liquid chlorine and occasional aeration to prop up the pH. (For reasons I don't understand, it tends to drift down even though everything else is balanced, but that's a different question for a different day.)

So the question is, all other things being equal (temp, sunlight, pool volume, other chemicals, etc.) does the FC level drop by a more or less constant AMOUNT per day, or at a relatively predictable RATE per day? With current conditions (hot & sunny) it drops 2-3 ppm/day regardless of the target level, but my data collection hasn't been stringent enough to do a proper analysis of amount vs. rate ...

Another option is to hack up a few 3" trichlor pucks and stick them in the Pool Frog that came with the pool but has been unused for years - I've done this before but never for such a long stretch of time.

Thanks in advance!

 

[HermanTX]

Welcome to TFP.
You may want to bump up your CYA to 50 to hold chlorine better against the UV.
Higher FC levels do burn off somewhat quicker but really you just want to estimate an average loss per day.
Let's assume 4ppm FC loss. So with a CYA of 50 your max SLAM level is 20ppm - refer to FC/CYA Levels
Also, you want to have a minimum of 4ppm when you return home. So 20-4=16. Therefore raising your FC to 20 you can be away 4 days (16 ppm divided by 4ppm loss per day) and it should be about 4ppm when you return. But you plan to be away 10 days.

You can ask a relative, friend, neighbor to come by on 4th day to add LC to bring it back up to 20 and/or you can add several pucks to a floater (using PM app) to supplement your FC loss plus it keeps your pH in check since pucks have acid in them.

I was away for the over a week during July 4th holidays and used both LC to SLAM level, had a neighbor add some LC after 4 days and also had 3 pucks in my floater. All was great when I returned home.

Edit - error on the high side since no one is swimming.

 

[jenrussell118]

Welcome to TFP.
You may want to bump up your CYA to 50 to hold chlorine better against the UV.
Higher FC levels do burn off somewhat quicker but really you just want to estimate an average loss per day.
Let's assume 4ppm FC loss. So with a CYA of 50 your max SLAM level is 20ppm - refer to FC/CYA Levels
Also, you want to have a minimum of 4ppm when you return home. So 20-4=16. Therefore raising your FC to 20 you can be away 4 days (16 ppm divided by 4ppm loss per day) and it should be about 4ppm when you return. But you plan to be away 10 days.

You can ask a relative, friend, neighbor to come by on 4th day to add LC to bring it back up to 20 and/or you can add several pucks to a floater (using PM app) to supplement your FC loss plus it keeps your pH in check since pucks have acid in them.

I was away for the over a week during July 4th holidays and used both LC to SLAM level, had a neighbor add some LC after 4 days and also had 3 pucks in my floater. All was great when I returned home.

Thanks for the welcome, validation, and real life experience - exactly the advice I was looking for!!