Chlorine and bather load

[bribri]

I understand the target and min levels of chlorine but how do I determine if i need extra chlorine for bather load.
Do I turn up the SWG before the party or after? Do I dose with liquid and how much? Last summer the water went cloudy after a few kids spent the afternoon in the pool. I think I may have had a low level algae problem even though the water was clear. As I remember the chlorine was 8-10 with cya at 60ish.

 

[Richard320]

I understand the target and min levels of chlorine but how do I determine if i need extra chlorine for bather load.
Do I turn up the SWG before the party or after? Do I dose with liquid and how much? Last summer the water went cloudy after a few kids spent the afternoon in the pool. I think I may have had a low level algae problem even though the water was clear. As I remember the chlorine was 8-10 with cya at 60ish.

Yes.

Run an overnight loss test (be sure to turn the SWCG off for it) to be sure you have no algae problem.

If I'm having a bunch of people in the pool, I'll dump in an extra quart or so (2 ppm) before they get there, and probably a half gallon after we're done. If I had a SWCG, I'd crank it up to max the whole time; it's safe to swim all the way to shock level, so there should be no problem.

 

[bribri]

Thanks, How many ppm per child? kidding. Ice just melted today in pool. Cool spring in Barrie Ontario

 

[chem geek]

A rough rule-of-thumb is that the chlorine demand from bather load in swimming pools is around 4 grams of chlorine per person-hour. In a 7500 gallon pool, this is only 0.14 ppm FC per person-hour. This is why you mostly see chlorine loss from sunlight being the dominant factor and not notice much change when there are just a few swimmers in the pool. However, if you have a pool party and have 10 people in the pool, then 1.4 ppm FC per hour is significant and even in a larger pool the demand would be noticeable.

Now if a child (or adult) urinates in the pool, then all bets are off since that's a much larger chlorine demand from one person. One cup of urine in 7500 gallons needs at least 0.8 ppm FC to oxidize it.

So Richard's advice of just bumping up the FC level by 2 ppm or so is usually sufficient and you can always monitor the FC level afterwards to see if you need to raise it higher. With CYA in the water, having a higher FC is not unpleasant.

 

[bribri]

I knew something was up when those kid stayed in the water all afternoon. I wish I could get some of that red dye that would expose who was urinating in My pool. Thanks for the info.

 

[linen]

I wish I could get some of that red dye that would expose who was urinating in My pool.

Urban legend