1/3 Water Replacement Resulted in Curious Water Chemistry

Jul 16, 2020
15
Augusta, GA
My primary problem was a salt level of 4800. My PB overestimated my pool volume and severely messed up my initial chemical balance. Since CYA was virtually 0, virtually everything else was way off, and my SWG didnt' seem to mind salt being 4800 ppm, I figured I could make it work.

So I spent the next few weeks balancing out my TA to 80 (down from 150), keeping my PH and FC happy, raising my CYA to 80 (maybe 90?), raising my CH to 275-300, and just dealing with my high salt level.

A few days ago, I began to worry about the high salt level as my water temperature rises. I don't want to drain my pool in July when water temperatures are 90+ and my SWG finally spits out the "high salt/high amps" error code. So I decided to tackle the problem now.

I drained 1/3 of my pool yesterday and here's the new puzzling issue: a lot of my water chemistry barely changed, despite my salt properly going down to 3200 ppm. My question for the group is this: do these numbers make sense? I've tested water 2-3x a week for 6 weeks and feel like I had a firm grasp on my pool's "behavior". I tested the new numbers twice today to ensure there were no anomalies.

Fiberglass, 11k gallons
AQR 940 TCELL15, OmniPL Automation
Prior to water replacement:
FC: 4.5
pH: 7.7
TA: 80
CH: 275
CYA: 80 (maybe 90?)
Salt: 4800

After water replacement:
FC: 4.5 (I purposefully ran my SWG to account for this)
pH: 7.7
TA: 70
CH: 200
CYA: 70
Salt: 3200

It seems too good to be true that I barely lost any CYA or TA.
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
7,751
NY
Hey Matt !!

did you test the fill water ? The CYA and salt dropped accordingly (I’m gonna guess your CYA was the 90). and if the TA, PH and Calcium of the fill water was somewhat close, they would not have changed much.

you can test the hose water now for an idea, although not the exact levels as it was at fill time.
 
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Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
7,751
NY
Looks about right to me with quick math. The CH dropped almost a third due to fill water at 25.

The TA was closer and dropped less.

The PH dropped a skootch but rose on its own right back due to the aeration of running the SWG to compensate for no/little FC in the fill water.

Anyway you slice it, Well done !!
 
Jul 16, 2020
15
Augusta, GA
I'd suggest you run your FC a bit higher as you're so close to the basement level required now that I fear one day you'll lose 1ppm too many and invite algae in to residence.
FC/CYA Chart

Maddie 🖖
The FC/CYA Chart has me at the target of 5ppm (SWG, CYA=70). Luckily with my TCELL15 and only 11k gallon pool, it's easier to overshoot the FC than undershoot. I'm watching it closely, as I anticipate the daily FC demand to be much higher than the current 1ppm as we get further into late spring/summer.

Thanks!
 
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