# SWG Run Time Calculator

#### mgmoore7

Bronze Supporter
What is the SWG Run Time Calculator?
A tool that is designed to answer the common question of "how long should I run my pump/SWG". It calculates the run time of your SWG and Pump based on your pool size, the output of your SWG and your daily FC PPM loss. It is designed as a starting point, not the final answer.

UPDATE 8/25/2016: I have completed a number of updates and integrated a suggestion from BestJoeyEver to be able to calculate the SWG % based on the desired pump run time. Here is a quick summary of the updates:
• Added change log
• Changed table to increment by 5% vs 10%
• Added calculation for SWG% based on desired pump run time
• Added basic instructions

Before starting your SWG, it is recommended to use Pool Math and bleach to get your FC to at least the target level. A few FC higher would be better until you dial in your SWG and you know that it is able to replace the 24 Hr FC Demand. The idea is to keep your pool from going below the minimum while you dial in the % and run time.

----ORIGINAL POST-----

Ok, so I am somewhat new and I have read over and over that it is just trial and error but I am still trying to get my SWG % and pump run time figured out. The trouble is that with every 1 hour of additional time or X % change, I don't really have any idea how much more chlorine that will produce in PPM for my pool.

So with known variables and possibly a few assumptions, could a formula be determined?

The goal of the formula would be to determine how long to run the SWG at 100% to get a certain output of PPM.

The variables that we know:

-X PPM loss per day (this would have to come from testing)
-Output of SWG (for example: "Pentair IC40.... will produce approximately 0.45 Kg of free available chlorine per 24 hour period"
-Pump run time
-Pool Gallons
-CYA

Has anyone tried to come up with a formula? What am I missing? On the surface, it seems that it should be possible.

UPDATE:
For those of you that want to try to the beta version of a calculator to determine SWG/Pump run time, below is a link to a Excel spreadsheet. Your feedback is welcome. It is designed to be a starting point, not the final answer.

UPDATE 7/20/2016: Added a new SWG Run Time Chart to quickly see various run time values at multiple % output and multiple FC demands.

Basic instructions:
1. Enter Pool Size in gallons
2. Enter your Average 24 hr FC (free chlorine) demand. (this value will likely be between 1 and 4)
3. Enter the amount of FC that your SWG creates in a 24 hour period. If you don't know, consult your instructions/documentation or click the link.
4. Enter percentage output that your SWG is set to. Suggest to start at 100%, then you can change the value to see the change in the run time.

Before starting your SWG, it is recommended to use Pool Math and bleach to get your FC to at least the target level. Higher would be better until you dial in your SWG and you know that it is able to replace the 24 Hr FC Demand. The idea is to keep your pool from going below the minumum while you dial in the % and run time. Pooldv's post #8 has good info on this. Also recommend the the following link: Pool School - Water Balance for SWGs

Your feedback is welcome. Just post to this thread.

#### pooldv

TFP Expert
Platinum Supporter
Moderator Emeritus
Re: Formula for SWG / Pump Runtime?

Yes, the manual states how many lbs of chlorine gas it will produce in 24 hours at 100%. Divide that by 24 and Use the Effects of Adding Chems toward the bottom of Poolmath to determine how many PPM x amount chlorine gas will add to your pool.

Koelest

#### JoyfulNoise

TFP Expert
Platinum Supporter
Formula for SWG / Pump Runtime?

Yes, the manual states how many lbs of chlorine gas it will produce in 24 hours at 100%. Divide that by 24 and Use the Effects of Adding Chems toward the bottom of Poolmath to determine how many PPM x amount chlorine gas will add to your pool.

^^ What he said....see here for a full feature comparison of all SWGs on the market -

Discount Salt Pool - Compare Chlorine Generators and Chlorinators

#### tucsontico

Re: Formula for SWG / Pump Runtime?

The biggest difficulty in determining an empirical formula is the first variable you list–the PPM loss per day. The chlorine dissipation will change from day-to-day based on the amount of sunshine on your pool, bather load, organic debris falling into the pool, etc.. Additionally, you aren't considering evaporation, which will have an effect, albeit small. One of the primary tenets among the members here is: "Every pool is different!"

Using the stated output of your SWG, you can get a starting point for your pump run time based on supplying a given amount of chlorine to hold the recommended level for an SWG system. You will be testing a lot during your first year of pool ownership! Once your pool has stabilized (there will be an increased MA use during the pool's curing that could last up to a year), you'll be able to dial-in the SWG to have worry-free sanitation. But only you will be able to get to that fine tuned state. Any stated "formula" will only get you close!

Good luck!

#### mgmoore7

Bronze Supporter
Re: Formula for SWG / Pump Runtime?

The biggest difficulty in determining an empirical formula is the first variable you list–the PPM loss per day. The chlorine dissipation will change from day-to-day based on the amount of sunshine on your pool, bather load, organic debris falling into the pool, etc.. Additionally, you aren't considering evaporation, which will have an effect, albeit small. One of the primary tenets among the members here is: "Every pool is different!"

Using the stated output of your SWG, you can get a starting point for your pump run time based on supplying a given amount of chlorine to hold the recommended level for an SWG system. You will be testing a lot during your first year of pool ownership! Once your pool has stabilized (there will be an increased MA use during the pool's curing that could last up to a year), you'll be able to dial-in the SWG to have worry-free sanitation. But only you will be able to get to that fine tuned state. Any stated "formula" will only get you close!

Good luck!

I agree with all that you have said but right now, the recommendation is to just start with trail and error and test daily. The issue is that while testing, manually additions of Chlorine may be required to ensure proper PPM and that further complicates the trial and error. A formula as a starting point as a minimum would at least help and then adjust from there. If the trail and error takes a week or more that is very likely, the PPM could easily fall below the minimum and then cause a need to SLAM....

I will be working on a formula in Excel. Maybe this can be my contribution to this community. We will see.

#### mgmoore7

Bronze Supporter
Re: Formula for SWG / Pump Runtime?

Version 1. I now see why my SWG is not keeping up. I have been running at 50-75% for 8 hours a day. That is not enough to replace the loss of 3-4 PPM per day.

#### pooldv

TFP Expert
Platinum Supporter
Moderator Emeritus
Re: Formula for SWG / Pump Runtime?

When I am dialing in my SWG with CYA at 80, min FC is 4 and target is 6, I dose my FC up to 8 or 9 and then try to get the SWG to maintain that. If it drops to 6 or 7 then I turn it up a bit. I pretty much never let my FC drop below target. One SLAM is all my pool will get!

#### mgmoore7

Bronze Supporter
Re: Formula for SWG / Pump Runtime?

V1.2

Do most SWG systems have a Output % that is adjustable?

#### JoyfulNoise

TFP Expert
Platinum Supporter
Re: Formula for SWG / Pump Runtime?

V1.2

Do most SWG systems have a Output % that is adjustable?

View attachment 51722

The Pentair IC only has 1% increments if the unit is paired with an EasyTouch panel. Otherwise the output is only adjustable in 20% increments.

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#### mgmoore7

Bronze Supporter
Re: Formula for SWG / Pump Runtime?

The Pentair IC only has 1% increments if the unit is paired with an EasyTouch panel. Otherwise the output is only adjustable in 20% increments.

Right, but I wonder about others. I have a EasyTouch. I was hoping to make this available to others but if the % output does not apply, the calculation may need to be changed.

#### mgmoore7

Bronze Supporter
Re: Formula for SWG / Pump Runtime?

When I am dialing in my SWG with CYA at 80, min FC is 4 and target is 6, I dose my FC up to 8 or 9 and then try to get the SWG to maintain that. If it drops to 6 or 7 then I turn it up a bit. I pretty much never let my FC drop below target. One SLAM is all my pool will get!
This is good advice and partially where i am going wrong. . I am going to the Target and that does not provide enough cushion

#### kywildcats

Bronze Supporter
Re: Formula for SWG / Pump Runtime?

V1.2

Do most SWG systems have a Output % that is adjustable?

View attachment 51722

My AutoPilot Digital can be adjusted at 1% levels, plus it automatically compensates for water temp changes.

#### pooldv

TFP Expert
Platinum Supporter
Moderator Emeritus
Re: Formula for SWG / Pump Runtime?

I believe that all SWGs except Intex have percentage output adjustments.

#### mgmoore7

Bronze Supporter
Re: Formula for SWG / Pump Runtime?

I believe that all SWGs except Intex have percentage output adjustments.

Great, thanks.

Here is the latest. Anything that I am missing? Obviously, the most difficult part is the PPM loss. I would think this could be measured over several days or a week and average it out. This would have to be done without the SWG running. Even that might not be right since there are alot of factors but it should be a decent starting point. Otherwise, maybe start with a value on the high side such as 3 or 4 and then back down from there.

If you want to download and take a look, here is the link: https://www.dropbox.com/s/xbrx61honuuu3jm/SWGCalculator.xlsx?dl=1

#### mguzzy

Gold Supporter
Re: Formula for SWG / Pump Runtime?

Yo Matt..
That is a cool calculator. I would love to see the equations in your spreadsheet. Great for dialing in the performance of your equipment. But here's the wrench in the gears. After going through my first SWG I found the FC production drops off with the age of the cell. In retrospect I noticed a difference with each year. And I don't know if it can be quantified. Since it really depends on how you treat your cell and the conditions it runs in. Even the state of the other equipment degrades over time (filters etc) and affects the performance of the other gizmos. When its hotter or you have more swimmers the output gets turned up. How often depends on your pool. I got 9 years out of my first cell, on this new one I'm going to try and run it on Super Chlorinate as little as possible and raise the FC by adding to the pool instead to see if that eases the load/lengthens the lifespan of the cell. who knows, as its a long term science/engineering project.

In the end it was an experiment each year. I tended to run the pumps for the same amount of time each day, but turned the % knob up on the SWG to compensate for the lower output. That's how I knew the SWG output was dropping each year. If I recall the drop off wasn't linear either, as the production tanked the last two years probably a sign the cell was getting grump and starting to fail.

#### tucsontico

Re: Formula for SWG / Pump Runtime?

V1.2

Do most SWG systems have a Output % that is adjustable?

View attachment 51722

Very nice job with the runtime/% calculator! This will definitely get folks "in the ballpark" for their SWG. I did a similar calculation based on my Pentair IC40 to get my pool dialed-in after installing the SWG.

#### Joey316g

##### Active member
Re: Formula for SWG / Pump Runtime?

This is great. Even with the famous "every pool is different line", it's nice to have something that gives you an idea.. A ballpark to be in.. Great job.

#### mgmoore7

Bronze Supporter
Re: Formula for SWG / Pump Runtime?

This is great. Even with the famous "every pool is different line", it's nice to have something that gives you an idea.. A ballpark to be in.. Great job.
Thank you. A ballpark is what I was looking for. It would at least shorten the trial and error. Ones i got the formula working, it instantly helped me realize I why it "was not keeping up". It just was not running enough. Mmn The

Probably need to document a process to calculate the daily FC PPM loss.

#### mgmoore7

Bronze Supporter
Re: Formula for SWG / Pump Runtime?

Yo Matt..
That is a cool calculator. I would love to see the equations in your spreadsheet. Great for dialing in the performance of your equipment. But here's the wrench in the gears. After going through my first SWG I found the FC production drops off with the age of the cell. In retrospect I noticed a difference with each year. And I don't know if it can be quantified. Since it really depends on how you treat your cell and the conditions it runs in. Even the state of the other equipment degrades over time (filters etc) and affects the performance of the other gizmos. When its hotter or you have more swimmers the output gets turned up. How often depends on your pool. I got 9 years out of my first cell, on this new one I'm going to try and run it on Super Chlorinate as little as possible and raise the FC by adding to the pool instead to see if that eases the load/lengthens the lifespan of the cell. who knows, as its a long term science/engineering project.

In the end it was an experiment each year. I tended to run the pumps for the same amount of time each day, but turned the % knob up on the SWG to compensate for the lower output. That's how I knew the SWG output was dropping each year. If I recall the drop off wasn't linear either, as the production tanked the last two years probably a sign the cell was getting grump and starting to fail.

In regard to the "wrench". I fully understand that there are variables that are unknown and change, this calculator is only designed to solve the "where do I start" question which is often the most difficult especially for those that are either new to their pool or new to SWG.

Lets take a example: I have read several times something like this to as a recommendation to start "every pool is different, start with 8 hrs per day at 50% and adjust from there". What if that only produces half of what is needed. If the pool owner does not start with a FC of higher than the target, the pool will quickly be under the minimum and then a SLAM may be required...

As I think about this.... We could recommend to get the FC to (Target + daily PPM loss + 1) after the daily PPM loss is known and then turn on the SWG. This way, you can dial in the SWG based on the results of the calculator while keeping the FC above the target. Once the performance and other variables impacting the PPM demand and SWG performance are known, the FC could be allowed to drift down a bit.

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