How I adjust my SWG (in addition to using PoolMath)

PoolBrews

Well-known member
Oct 16, 2019
486
The Villages, Florida
Pool Size
6750
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite Pro (T-15)
I have posted numerous times over the past 2 years (ever since we installed our first gunite pool - 1st two were vinyl liner) concerning my issues with having to SLAM my pool about once every month or two. I received a ton of advice here on TFP. All of it made perfect sense, but I still struggled to keep from having a hazy pool on a regular basis.

I wanted to share what has finally worked for me. The issue stemmed from two specific items:
  1. My CYA here in central FL changes far more frequently than it did in either MI or GA. Especially after a heavy rain (which we get a lot of here). I was used to checking CYA about once a month in MI or GA - now I check it weekly here FL. In addition, in MI or GA, if CYA went to 60, no problem - here in FL it really NEEDS to stay at 70 or 80.
  2. Caused by not performing #1 often enough, when I would start to see my chlorine drop, I would turn up my SWG in hopes of averting an upcoming SLAM. This would work for a few days to a week, and then finally the SWG couldn't keep up.
Since I have been checking my CYA weekly, I'm now on 4 months and counting without a SLAM. During this journey, I wanted more info available than PoolMath currently provides. I created an Excel spreadsheet to track the same data I enter into PoolMath and added a method of displaying my chlorine loss since last check (based on SWG run time), my chlorine loss per hour, and finally the true SWG % needed to counteract the loss. This helped me tremendously while figuring this out. I'm including my addition here as I feel this is something beneficial that could be added PoolMath.

Shown below are 3 columns. The 1st column is the date point being collected/calculated. The 2nd is readings from day 1, and the 3rd from day 2.
Free Chlorine
13.5​
10.5​
CC
0​
0.5​
Salt Cell %
5%​
10%​
Time Stamp
10/22/21 13:27​
10/25/21 12:05​
SWG Start Time
9:00​
9:00​
SWG End Time
21:00​
21:00​
SWG # Hours
22​
35​
Total # Hours
46​
71​
Loss Since Last Check
1.5​
3.0​
SWG Add
2.4​
1.9​
Loss w/SWG
0.9​
4.9​
Total Loss/Hour
0.04​
0.14​
% Req to Generate
4%​
13%​

My SWG start time and end time are consistent from day to day, so this doesn't change. Once I enter in my FC, I then enter a time stamp for when the sample is taken (this is already done in PoolMath). From here, everything is calculated. The current time stamp is compared to the previous time stamp. Total time and the total SWG run time since last collection are calculated. The SWG % is pulled from the last test results set. Using current FC reading, last FC reading, and FC added by SWG, this shows total FC loss, and how much was really lost when adding in the amount added by the SWG.

Finally, it then shows the % I should set my SWG to to maintain the current FC level. This is specific to my SWG and my pool (which PoolMath also knows).

If I do change my SWG setting after the reading, I enter in the new % for that day's reading.

I know it looks like a lot of data, but to me the really helpful value is the "% Req to Generate". It took a lot of guesswork or calculating out of this process for me.

If anyone is interested, I can share my spreadsheet with the calculations built in
 

Newdude

Mod Squad
Gold Supporter
TFP Guide
Jun 16, 2019
18,178
NY
That’s GREAT news PB !!! Many folks have seen the CYA break down in warmer temp, and you certainly apply in FL. Did we ever look into your phosphates ? While they are no concern for 99% of pool owners, they still matter for a lot of folks. In 2020 there were 10M pools on record in the US. With the 99% spitball estimate that’s still 100k folks that may need to look into them.

It won’t hurt to keep tabs on it as extra insurance. We can’t talk about it upfront with everyone as far to many newbs come in grasping at straws and hoping that they are ‘the one’. Doing so would give credit to the bad advice they are already clinging to, but phosphates do matter fo a select few.
 

TampaKathy

Gold Supporter
Oct 2, 2020
795
Tampa, FL
As a fellow Floridian, I wouldn't mind having the spreadsheet...I don't understand it right now...but very soon I will have water in my pool and I'm sure it will make more sense when I start testing. Now to go google "Phosphates" to see what I should be worrying about ;)
 
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