SWG run time calculations assistance

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sbcpool

Well-known member
Mar 10, 2015
728
Upland, CA
I've quadruple checked my calculations and tested and re-tested at least a half-dozen times over the last three days and there is something I'm clearly messing up or not understanding.

I installed my first SWG over the weekend. It's a CircuPool RJ60+. The unit is advertised as capable of producing 3.1 lbs./day of chlorine. By my calculations that is 1406 grams per day, or about 58.5 grams/hour at 100%. In my 20,000 gallon pool that should raise FC by 0.77 per hour.

I have the RJ60+ set at 100% and a pump run time overnight of 4 hours. Based on the above calculations I should see +3 ppm FC in the morning. I'm not seeing that at all. It's more like 1 ppm or less. My pool's measurements are:

Salinity: 3800
Temp: 82°F
CYA: 50 ppm
pH: 7.5
FC last night: 5.5
FC this morning: 6.5

My very first thought was, "something's eating the chlorine overnight," but the time between when the pump turns off and I wake up and test the pool is about 3 hours. Something would have to "eat" 2 ppm worth of chlorine in three hours but leave it alone the rest of the day to leave me with 5.5 in the evening. I even re-tried the tests (CYA and FC) using chemicals I received a couple weeks ago direct from Taylor with the same results. I went out to get a salt test kit (only strips available locally) to confirm the SWG's measurements and they agree. There's something I'm missing here. Luckily I bought a giant vat of FAS-DPD reagents so I'm going to run detailed tests (25 mL for 0.2 resolution) throughout the day to watch FC like a hawk for a day or two.

I switched on the pump at 06:10 PDT to run for an hour and test again. I'll report back.

This is reminds me of those days when I first inherited the pool and had zero idea what I was doing :(
 
Filled two tests to 25 mL, one from farthest from returns and one sample right near a return. Both took 31 drops, or 6.2 ppm.

Bubbles are coming from the returns and the SWG cell is clearly working by observing the bubbles produced inside.

I am letting the pump run another hour.
 
This issue can be distressing. :brickwall: I know because I was concerned about my 45+ a couple weeks ago and it's new as well. So here's what I learned with mine:
1. I monitored my FC testing VERY closely for about a week. Water sample from the same place, tested at the same time, etc, to see if the FC was holding or going up/down.
2. I ruled-out algae. I passed an OCLT with no problem.
3. I double/triple checked my CYA. When my CYA is below 70, the FC simply doesn't seem to hold as well, especially with intense sun and heat.

Once you do those basic things, if you still find that the FC isn't being produced as expected, you can contact Cirupool. They will probably ask you a couple basic questions, the same ones in the manual about phosphate control (boo!) and possibly scale, but yours is brand new, so scale shouldn't be an issue. So before you panic, I would keep a close record of your FC results for a few days. You might go ahead and increase the CYA to at least 70 now if you are sure you are algae-free. If you have any doubt about algae, run an Overnight Chlorine Loss Test first. Then you should have a much better idea about the performance of the cell.
 
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I’d suggest running an OCLT test. Leave the SWG off tonight and test the chlorine in the evening and in the morning and see if there is any chlorine loss. That way you will know whether you are losing chlorine overnight or if the SWG isn’t generating as much as you are expecting.

We can figure out what to do next based on the results from that.
 
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Thanks guys. Right now I'm establishing production numbers with this 2-hour run test. I will switch it off for tonight and see how the last reading of the day compares with tomorrow morning to see if there is an FC demand that's affecting today's production testing.
 
sbcpool said:
Thanks guys. Right now I'm establishing production numbers with this 2-hour run test. I will switch it off for tonight and see how the last reading of the day compares with tomorrow morning to see if there is an FC demand that's affecting today's production testing.
Click to expand...

For what it’s worth, test runs during the day can be difficult because the UV from the sun will consume some chlorine, so it can be difficult to determine exactly how much the SWG is producing. I would suggest doing your tests overnight, first starting with a chlorine loss test without the SWG running to make sure you don’t have algae consuming your chlorine overnight.
 
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Strange. The previous result suggested that there was no increase between 06:10 and 07:10, but I just tested twice again and got 7.8 ppm, which is in line with what I'd calculated I should have seen in two hours' run time. Maybe it takes an hour for the water to get moving and mixed up, although I did take a sample from right near the returns too. Who knows?

Now I'm letting the pump run without SWG for another hour to make sure everything's good and mixed. I'll report back this evening after the pool is in shadow again to begin the OCLT.
 
Keep in mind that the RJ's have a duty-cycle that is 180 or 200 minutes (I have read conflicting reports on the time). So at 100%, it will only generate for 180 or 200 minutes and then stop chlorine production for a set period of time. As you adjust the output, this also changes the duty cycle...thus if you set it at 75%, it would stop producing at 135 or 150 minutes.

When I was trying to figure mine out (I have had it installed about a week and a half) I did use my own math (using the RJ 3.1 lbs number) and also the SWCG math app that is on the forum and started from there. When I ran the pump at 6 hours, it was *only* producing about 1/2 of what the calculations were telling me. Taking consideration of the duty cycle, I split the cycle into two cycles (3 hours each) and then the production numbers got closer (but not exact) to what was calculated. Oh, just for anecdotal evidence, I have my RJ set at 75%.
 
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That's good to know. I assume when they claim 3.1 lbs/day they are taking that duty-cycle into account.

The entire reason for going with the CircuPool was because it could produce the necessary amount of chlorine within my usual 4-hour run time. I don't mind running a little longer, but if I have to run 8 hours to get their claimed output I would feel like I was scammed.
 

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HeyEng said:
Keep in mind that the RJ's have a duty-cycle that is 180 or 200 minutes (I have read conflicting reports on the time). So at 100%, it will only generate for 180 or 200 minutes and then stop chlorine production for a set period of time. As you adjust the output, this also changes the duty cycle...thus if you set it at 75%, it would stop producing at 135 or 150 minutes.
Click to expand...

This is not quite true. At 100% it generates nonstop for as long as it’s powered on. It’s only at less than 100% that the duty cycle comes into play. I believe the 180 minute duty cycle is correct, so at 75% it would generate for 75% of 180, or 135 minutes, then it would be off for 45 minutes. At 50% it would generate for 90 minutes, then be off for 90 minutes.
 
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That's good information to have. Depending on your pump run time you might have to set the unit in a way that was different than calculations might suggest. In my case, with a 4-hour run time, if I actually needed a real 75% (180 minutes of output) setting it at 75% would actually give me 81.25% (135 minutes on, 45 off, 60 on = 195 minutes on). I would have to set the control unit to 70% (126 minutes on, 54 off, 60 on = 186 minutes on).

Interesting.
 
Brett S said:
This is not quite true. At 100% it generates nonstop for as long as it’s powered on. It’s only at less than 100% that the duty cycle comes into play. I believe the 180 minute duty cycle is correct, so at 75% it would generate for 75% of 180, or 135 minutes, then it would be off for 45 minutes. At 50% it would generate for 90 minutes, then be off for 90 minutes.
Click to expand...
Ah, good catch...thanks.
 
I am just the opposite with my SWG.. I run the pump and SWG long enough to get the FC to the level I want... if it is low at 4 hours go to 6 and see if that works... With the sun, wind, your pool water, the bird flying over and so many other reasons the FC use can change from day to day... I get it close and I am done... I know the math is supposed to be close but....

I run 4 to 6 hours spring and fall and 8 to 9 hours summer
 
This is what helped me. Shock your pool with liquid chrloine to 10ppm. Then over the next 2x days let it come down and determine how much loss you have. Then use pool math and to figure out the value to replenish the loss. Then wait till it goes to the middle and turn our SWG back on. It will go up during cloudy days and down during sunny days but it will cover you.

Sunny days 2-2.5ppm loss with 60cya. cloud days or days when I have my cover on 1-1.5ppm. Not exact science but it gets me close. SWG is not a set and forget that was the lesson I learned. It would be nice if the SWG's had a FC probe.

Hope that helps
 

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