New to me pool - FC keeps increasing after being stable for several days, was SWG output just too high?

WoodenNickel

Silver Supporter
Jul 1, 2021
9
Granbury, Texas
Pool Size
14000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
We recently bought a house with a pool, and found out that the SWG wasn't working and FC was at zero when we moved in. After adding LC, we got the FC up to 5.5, quickly thereafter fixed the SWG, and things seemed stable for at least 5 days. Recently FC started creeping up, and I lowered the SWG output a couple of times, and the FC kept rising. I'm curious if the initial SWG setting was really just overly high, or if I'm missing something else that's going on?

Full data is in my pool math logs, but at a high level:

3/31 - FC = 0 ; added LC to get up to ~8 FC
4/4 - SWG fixed ; set at 65% which is where it was when we bought the house
4/6 - FC = 5.5
4/8 - FC = 5.5
4/14 - FC = 8 ; Changed SWG output from 63 to 50
4/16 - FC = 9.5 ; Changed SWG from 50% to 45%
4/17 - FC = 13.5 ; Changed SWG from 45% to 30%. Turned SWG off completely until FC gets in a lower range. If it matters, this was the first day we swam in the pool (wahoo!), so there was load from people for the first time in addition to what's in the pool math logs.

I have added Muriatic Acid a couple of times to address PH/TA, but my understanding is that doesn't impact FC.

The SWG is a Hayward TCELL940 and runs on a single speed pump for 10hrs a day, and the pool is about 14k Gal. Can somebody more familiar with the math involved let me know if the 65% SWG output it started at was just crazy high, or is there a better explanation to the rise?
 

Flying Tivo

TFP Guide
Jan 24, 2017
2,656
Monterrey, NL, Mexico
Pool Size
7500
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
If its a T-9 cell then you should be running 50% for 10hrs to produce 2ppm of FC which is in the range of 2-4 consumption of regular pools.
The only explanation could be bad testing, intermatic timer issues, or that initially you had a start of algae and you took care of it with high levels of SWG. Let it drop back to 5 and start your SWG at 50% and go from there. Also reconfirm your pool volume.
 

WoodenNickel

Silver Supporter
Jul 1, 2021
9
Granbury, Texas
Pool Size
14000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
If its a T-9 cell then you should be running 50% for 10hrs to produce 2ppm of FC which is in the range of 2-4 consumption of regular pools.
The only explanation could be bad testing, intermatic timer issues, or that initially you had a start of algae and you took care of it with high levels of SWG. Let it drop back to 5 and start your SWG at 50% and go from there. Also reconfirm your pool volume.
My understanding is the TCELL940 is an extended life T15 cell, so I assume I'd expect to be even further under 50% usage?

There water has been visibly clear with CCs at zero mostly (0.5 the last couple of days), so no outbreak I'm aware of. The timer seems consistent, comes on around 8am, and off around 6pm. I am new to testing, but feel pretty good about it and have been doing it consistently. PB confirmed the sizing, and that math when adding acid a few times seems to pan out, so I suspect it's in the ballpark.

Sounds like I'm likely on the right track. I'll keep a close eye on FC, and start the SWG back up around 5 and see how it goes. Thanks!
 

mgtfp

Silver Supporter
Bronze Supporter
Mar 5, 2020
1,336
Melbourne, Australia
Pool Size
66000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Astral Viron V35
How was the weather like in the previous days, how much sun does your pool get? Was it sunny during the period when FC was stable, and now it's cloudy?
 

markayash

Gold Supporter
TFP Guide
Mar 21, 2016
4,063
Atlanta Ga
Sounds like you’re on the right track, just test and adjusting it.
As the water temp goes up you might have to bump it up some.
But the biggest thing is don’t make my mistake and try to keep it near the min level 😎. SW pools aren’t as sticky feeling to me so a higher FC isn’t a bad thing.
 
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