Please check my math for Chlorine consumption

[Foonly]

I am gradually adjusting my new SWG to maintain a constant FC. I figured that if the FC, TA, and CYA are constant over 24 hours then I am adding Chlorine as fast as the Sun etc is eating it, so I set about to calculate how much that was. (Log is in my profile)

The cell is rated at 1.45 pounds of Chlorine gas per day at full power. I am running it at 9% over 24 hours which gives me 0.131 pounds per day. The pool is 10,400 gallons which should weigh 10,400*8.33 pounds or 86,632 pounds. (That is not corrected for temperature, which is about 90 degrees) So if I have this right, Chlorine parts per million would then be 0.131/86632*1E6 or 1.52 ppm.

Surface area of the pool is 12x29 feet or 348 square feet and it gets direct Sun about 4-5 hours per day. Is 1.52 ppm a reasonable amount to be adding? (Side note - the energy going into the pool from the Sun is about 150 KWH per day, which is twice my house electricity consumption! Too bad I can't capture that.)

By having this number, I should be able to adjust the FC at a predictable rate knowing that 9% power => 1.52 ppm.

 

[Leebo]

Save some headaches.......use PoolMath ?

 

[setsailsoon]

Foonly,

You can use Pool Math for this. Set it for SWG chlorination then go to the "effects of adding" select swg for chemical to add and select your brand and model. I get 30% for 7 hr pump run gives you 1.5 ppm using my swg that has 1.5 Lb/day output...should be close to yours. *** Edit: Just saw Lee did the Pool Math while I was typing for yours at 24 hrs I get 1.6 ppm using your 24 hr as expected a little higher***

Hope this helps.

Chris

 

[Foonly]

At least this confirms that I understand the math properly! Thank you. Now should I want to increase FC by 2 ppm per day, I would set the power knob to (1.54+2.0)*9/1.54 = 21% then when it reaches the desired level back it off again to 9%.

 

[setsailsoon]

At least this confirms that I understand the math properly! Thank you. Now should I want to increase FC by 2 ppm per day, I would set the power knob to (1.54+2.0)*9/1.54 = 21% then when it reaches the desired level back it off again to 9%.

Or just use Pool Math for each desired change. You can set it to predict each of the variables. It will make you lazy pretty quick.

Chris

 

[Foonly]

Shouldn't the SWG power setting be exactly the same in the steady state, regardless of FC level? I would think that the power setting controls how fast it changes, not what it settles at.

 

[setsailsoon]

Shouldn't the SWG power setting be exactly the same in the steady state, regardless of FC level? I would think that the power setting controls how fast it changes, not what it settles at.

Well, sort of. You can adjust run time also. % power and pump run time both affect how much chlorine is generated. They don't control to a FC content of the water. So you have to calculate the settings required. Pool Math is very accurate for this but all pools are different. So the actual production needs to be increased and decreased as chlorine demand changes. I've found the easiest way to do this is to set for my target FC level and let it fluctuate. When it trends down as summer heats up I'll add a little run time. You could do the same thing with % power so long as you have the ability to make fine adjustments. Some SWG's without automation only change in large increments on % power.

I hope this helps.

Chris

 

[Foonly]

Yes, that is the approach I have been taking - small changes. I can adjust power in one-percent increments. FC has been trending low the last two days so I increased power to a level that should result in a +1 ppm change per day to bring it back into the desired range. Also found CYA was a bit low so added that. TA is starting to edge down too so keeping an eye on that.

Some days the pH has zoomed up to 8 and other days hardly changed at all. Not sure why that is yet. The pool gets pretty consistent small usage.