Interesting Chlorine Results

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eqbob

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Jul 25, 2012
436
Central Texas
So I've been testing Chlorine now using the FAS/DPD test. We started off with FC at 9 with the salt cell running at 60%. Kicked to 50 and then 40% with no change in FC. Using 10ml sample so each reagent drop equates to 0.5.

I then dropped the salt cell to 25% and saw the FC decline to 8.5. Excited since that's been the first discernible change.

So a couple of questions.

Does the amount of powder in the scoop matter greatly? I'm guessing not as they would provide a more exact way to measure because that scoop is small and you could easily get 2x the amount of powder you'd need if you just dip and pick. But if so, this could account for things.

So if this is a discernible change, I wonder how low I could/should go on salt cell. I know I could go to 0 physically.

The only othe thing that would affect the production would be the flow rate of water through the cell and the time that the pump is on, right?

I'm not "worried" about having too much chlorine because botching with grow then and I'm good with that...lol. But there no reason to burn out the salt cell before its end of life...

Other readings of interest:

ph 7.6. Was 8 but added muriatic to drop it)
CH 300
TA 70
FC 8.5
CC 0
CYA 50
BTW, confirmed FC range by using the other test with the color comparator and was in the 5-10 range. Also CC was 0 there as well.
 
This is my first year with an SWG and I'm having the same problem. My FC has jumped from a consistent 6-7 during the summer to 9 recently. I've cut my SWG run time by more than half over the last month and still have high FC test results.

I think shorter and cooler days and lower angle of the sun, together with drop in pool water temp from 80s to low 70s must have significantly reduced FC degradation. I'm keeping a log of SWG settings so I'll know better what to use next year.
 
So what are people using for their percentage then with the lower demand? My decrease has been over about 10 days. Just took it to 25 percent yesterday. I guess the good thing is that we know nothing is going to grow in there....lol
 
eqbob said:
So what are people using for their percentage then with the lower demand? My decrease has been over about 10 days. Just took it to 25 percent yesterday. I guess the good thing is that we know nothing is going to grow in there....lol
Click to expand...
I think pump run time and %cell on time are the only things that determine FC generation. As long as the SWG minimum flow is exceeded I don't believe additional flow changes the amount of FC generated by the cell. However if at lower flows you get a lot of bubbles at the returns it's possible chlorine is being lost in the bubbles.

I can only change my cell in increments of 20%, my last change was from 40 to 20% so that cut cell run time by 50% !!! Next step would be to cut pump run time but I'm already down to 3 hours per day.

In order to decrease a high FC reading you actually have to set the SWG so that it generates less chlorine than is being consumed in the pool. Of course you then overshoot to the low side and have to adjust back up. I'm thinking that with a high FC it would be quicker to turn the cell off for a few days until FC drops back to normal, and then turn it back on at the new setting. Test results over the next week or so should show if the new cell run time is close to where it needs to be.
 
That's an interdting thought I guess. Could do that. Probably have to watch it pretty carefully to ensure you don't get down to 0 much faster than anticipated and start an algae problem. Althought, as the water gets lower and lower into the 70's, that's less likely to occur.
 
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