Tweaking either pump run time or SWG % to get to optimum FC level

[ping]

Most SWG's reverse the polarity every now an then which helps keep the cell clean. Even with this feature, cells will build up scale which doesn't come off if the CSI is in the positive range long enough. Depending on how high the pH got above 7.8 your numbers indicate that it could be subject to a light build up of scale. Right now I don't think that is the issue and you just need to turn up the % and/or run time.

 

[JoyfulNoise]

For giggles I upped the CH to 5 (recommended level for my CYA) and I'm going to keep SWG and pump time as is and monitor for the next few days. I cannot imagine that my SWG @ 75% cannot maintain 5 ppm. I'll update with my experience.

NOTE - Please use the terminology "FC" or "chlorine" for bleach additions. "CH" means calcium hardness and you'll just confuse everyone if you use that.

Let's just do a little math (PoolMath really) -

IC40 daily production rate - 1.4lbs Cl per 24 hours

So, if you run 8 hours at 75% power you get -

(1.4lbs-Cl(g) / day x 16 oz / lbs) * (8hr / 24 hrs/day) * 0.75 = 5.6 oz of Cl gas

If you plug 28,000 gallons into pool math and go to the bottom section entitled "The Effects of Adding Chemicals", put 5.6 in the field and select "Chlorine Gas", then you get -

raises FC by 1.5, lowers pH by 0.12 and raises salt by 1.2

Standard daily loss rate of FC for a clean pool in full sun can be anywhere from 2-3ppm/day or as much as 4ppm/day if it is really hot.

Therefore, your net rate of FC loss/gain is going to be -

FC(added) - FC(lost) = Net FC per day

1.5ppm/day - 3ppm/day = -1.5ppm/day

So even if you increased your output to 100%, you'd still only have an FC input of 2ppm/day which would barely compensate for your FC loss to sunlight, etc.

Bottom line - you need to run your pump for more hours OR at a higher speed to circulate more water through the IC40.

 

[QingGuy]

@joyfullnoise - Thank you so much for taking the type to run that. I'd never seen the bottom section of pool math, just never scrolled down that far. Takes all the guessing "tweaking" out of it. Thanks again for pointing this out to me. Pool Math is even cooler than I originally stated!