Calculating the PPM FC from my SWG

red-beard

Gold Supporter
May 27, 2019
557
Houston, TX
I have adjusted my pool size to 25,000 gallons, based on my best calculations for the pool (24,665) and the equipment ~ 25000 should be within 1%.

This is 208,500 lbs of water. My SWG can generate a maximum of 1.47 lbs/day of chlorine. If all of this if FC, it should be 1,000,000*1.47/208,500 or about 7 ppm each day at 100%.

My typical need is around 3 ppm, so my initial setting is 50%, or a little over. I also need to raise my 30 CYA to at least 60 CYA. I'll start that tomorrow.

This sound about right?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,003
Laughlin, NV
As summer comes to a close your FC use will fall. But expect it to rise again next May or so and 3-4 ppm per day will be very normal.
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
19,132
Bedford, TX
James (Red),

Why do you run your pump so fast??? A SWCG either works or it doesn't.. More water does not make it produce more chlorine. As long at the flow switch is closed you are good..

I run my pump at about 1200 RPM, not sure what that is in GPM, but I doubt it is anywhere near 40...

Raising your CYA will have a big impact on how much FC your pool uses each day.. My first indication that my CYA is on the low side is when my FC demand goes up.

Thanks,

Jim R.
 

red-beard

Gold Supporter
May 27, 2019
557
Houston, TX
James (Red),

Why do you run your pump so fast??? A SWCG either works or it doesn't.. More water does not make it produce more chlorine. As long at the flow switch is closed you are good..

I run my pump at about 1200 RPM, not sure what that is in GPM, but I doubt it is anywhere near 40...

Raising your CYA will have a big impact on how much FC your pool uses each day.. My first indication that my CYA is on the low side is when my FC demand goes up.

Thanks,

Jim R.
I'm running 1050 RPM = 40 GPM, and about 55 Watts. I guess I can reduce the speed further, since it only needs 11 GPM to run.

If your 3HP VS pump is the Intelliflo, then based on the pump curve I think you're running more than 50 GPM. What is your back pressure at 1200?

3HP intelliflo.jpg
 
Last edited:

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
19,132
Bedford, TX
James (Red)

My filter pressure is about zero or 1 lb... at 1200 RPM..

I really doubt that you are moving 40 GPM at 1000 RPM, but then I've been wrong about a 100 times today alone.. :mrgreen:

But to find out for sure you will need to talk with some our flow dynamics guys.. There is a lot more to it than the pump curve..

Anyway, if you are running at a 1000 RPM then I take back my comment on you running your pump too fast.. :)

Thanks,

Jim R.
 

red-beard

Gold Supporter
May 27, 2019
557
Houston, TX
I tried to install a flow meter from TFTESTKITS in the check valve on the pump, but it turned out I have 3" lines out of the pump! At some point, I'll order the inline meter.

If the pressure gauge is close to the pump, you should be able to read the flow from chart. The gauge is reading the pressure rise across the pump. It is surprising that the low speeds actually produce quite a bit of flow. But it is because of the very low head. I run 24 hours at low speed for the better cleaning on the filters.
 

red-beard

Gold Supporter
May 27, 2019
557
Houston, TX
8/29/2020 - 7:15 PM - FC 4.6 ppm
0/30/2020 - 7:15 AM - FC 5.8 ppm

It looks like it is working as advertised. I will let it run at 35% today and see where we end up.

I have some bubbles from a couple of the returns in the hot-tub. There are 11 returns in my pool, 6 are in the hot tub. The hot tub, by pipe, is at least 60 feet from the SWCG. No bubbles from the pool returns, even the close ones. I expect this is "normal", but probably is reducing the efficiency of the SWCG somewhat.

Hmmmm. @100% 1.47 lbs/day, @35% 0.5145 lbs chlorine/day = 233.37 grams. @ 35.453 g / Mol

6.58 Mols of chlorine @ 22.4 liter/mol = 147.45 Liters of Chlorine gas per day at 35% setting. The bubbles are probably not significant.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,003
Laughlin, NV
Ha!! It is pretty neat to take one of those extended BBQ lighters and put it next to the bubbles coming out. You can get them to snap occasionally.

That is why it is very important to remove the power from the SWCG when the pump is not running. If the flow switch fails and the SWCG generates and hydrogen gas builds up things go BOOM!
 

red-beard

Gold Supporter
May 27, 2019
557
Houston, TX
Ha!! It is pretty neat to take one of those extended BBQ lighters and put it next to the bubbles coming out. You can get them to snap occasionally.

That is why it is very important to remove the power from the SWCG when the pump is not running. If the flow switch fails and the SWCG generates and hydrogen gas builds up things go BOOM!
Oh the Huge Manatee!

huge mannity2.jpg
 

red-beard

Gold Supporter
May 27, 2019
557
Houston, TX
8/29/2020 - 7:15 PM - FC 4.6 ppm
8/30/2020 - 7:15 AM - FC 5.8 ppm
8/30/2020 - 7:15 PM - FC 4.0 ppm

At 35%, the unit should be producing 7 ppm * .35 = 2.4 ppm FC. My chlorine dropped by 0.6. So my "need" was 3.0 ppm.

New setting: 35% * 3.0 / 2.4 = 43%. Pool Math agrees.

Everything is rounded to nearest...

This is at 30 ppm CYA. Next I will be adding 6 lbs of CYA and see how that affects my CYA (~60) and FC demand.
 

red-beard

Gold Supporter
May 27, 2019
557
Houston, TX
I added CYA last night. Tests show a 60 ppm CYA now. With the 43% that was just "holding" in a 24 hour cycle, with the CYA, I stayed at 5.0 ppm FC from this morning to this evening! Charts says to hold at 4.0 ppm FC, but I'm going to keep it at 6 ppm since I'm paranoid about mustard algae. I'll retest CYA tomorrow to see if it goes up.
 

setsailsoon

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LifeTime Supporter
TFP Guide
Oct 25, 2015
3,383
Stuart/FL
Red,

Staying a little above target has always worked great for me. If your pool's anything like mine getting your CYA up will help a LOT.

Chris
 

red-beard

Gold Supporter
May 27, 2019
557
Houston, TX
It's been very hot and sunny here, so I hope this is a good test. I'll keep the CYA at 60 and see how it does. There was definitely a steep decline in the chlorine loss. Usually there is a loss of about 3.0 during the day. Starting at 5.0, +1.5 production and a loss of 3.0, I should have reduction of 1.5 ppm. Staying at 5.0 means my loss was only about 1.5. I'm going to drop it to 30% tonight so I only gain 1 ppm overnight. If that holds true, I'll adjust it down to 22% in the morning, so I produce 1.5 ppm over 24 hours. I should cycle between 5.25 and 6 ppm.

And then I have to figure out what to do with my extra time!
 
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