How chlorine to get to level (ie how much to run SWG)

[doncaruana]

I know it's mostly "play around with it until it's good", but I like to have a "refined" target, if you will, for things.

So, doing some reading, I think to get to 3.0 ppm of free chlorine I think I would need .4 lbs of chlorine. This is based on 16000*8.34 (lbs/gallon of water) = 133,440 pounds water and if I multiply that by .000003 (3 ppm), I get .4, or 6.4 ounces.

Does that all sound right or am I way off?

Because, if that's the case, my SWG tells me how much chlorine it's supposed to produce and I have my target. The IC40 says running full tilt it will produce 1.4 lbs of chlorine in 24 hours. So, if I ran my pump for 7 hours at 100%, that would give me my target.

Do those numbers sound rational?

 

[JasonLion]

You are doing your math right, but solving the wrong problem. When adjusting a SWG, you aren't trying to raise the FC level from zero to the target level, rather you are trying to replace the chlorine lost to bathers and sunlight. That amount varies with the weather, the number of swimmers, and so on, and can not be calculated in advance.

 

[doncaruana]

Well I'm doing something right!

Thanks - it never occurred to me that I was solving the wrong problem.

However, that sort of segues to a companion question - when is the best time to measure the chlorine? So far two afternoon readings were 0 and a morning reading was 1.

 

[duraleigh]

The FC will be the lowest in your pool usually around late afternoon or after a heavy bather load. Check it then to make sure you have not gone too low but also check it at other times occasionally to see how uniform it stays in a 24 hour period.

 

[ping]

It is usually best to bump up the chlorine level to your target level with bleach when the FC gets too low. This way you will get your FC up quickly and will not have to rely on the SWG to raise your FC.

 

[OperatorX]

Just to give you some comparison information. I have an IC-40 & a 20K gal pool. During July and August last year (pool startup late June) I was able to maintain 3-5 ppm on the 60% setting, running from 8 am -8 pm. My pool gets sun all day and kids swam most everyday. The 60% setting was probobly higher than it needed to be because I was not measuring CYA accurately. I got the test kit here and will be better able to track that better. With that said, that same setting covered the swings (rain, clouds and such) pretty well. If I knew a rainy period was coming and the kids would be out of the pool, I'd super chlorinate just to give it a boost. Had to do that during the hurricane that came up the eastern seaboard last September. I keep bleach handy to shock when needed but will probobly be able to run it less this year, at a propper CYA level (60-70).