Two identical pools- Hypothesis?

[Rangeball]

Imagine you have two identical pools, side by side. Same volume, equipment, water chemistry, exposure to dust/pollen, etc.

Both pools circulate overnight. FAS/DPD testing shows 3 ppm FC with no CC first thing in the am. CYA is 25 ppm.

Pool A is allowed to circulate throughout the day. Pool B has the pump turned off, so it is sitting stagnant in the sun.

Later that evening Pool B is turned back on and allowed to thoroughly circulate and mix, then both pools are FAS/DPD tested again.

What would you expect to find?

Pool A has thoroughly mixed water throughout the day, possibly allowing minimal CC to briefly form. However due to circulation, the deeper "protected" water is mixed and brought to the surface throughout the day.

Pool B, by sitting stagnant, had the top layer of water exposed to more sunlight, probably more CC created but the underlying water that was "protected" was, well, protected

What do you think the outcome would be of the testing at night?

 

[JasonLion]

I would not expect the differences to be significant, but you might be able to measure something. I would expect pool A, daytime circulation, to have lost slightly more chlorine and to have an ever so slightly lower risk of algae. Chlorine will be lost from the surface layer more quickly than by the deeper layers. If the surface layer is constantly replenished by circulation, more total chlorine will be lost. Again, I would expect any difference to be small.

 

[Rangeball]

Jason, that's the conclusion I came to as well.

I'm wondering about my pool. I have been running my pump during the night from 8pm to 8 am, so it can circulate when I add bleach.

I tested this am and had 3 ppm FC with 0 CC. I left the pool circulating and will check again this evening at sundown. Tomorrow morning I'll test again, turn the pump off then back on a few hours before sundown and test again.

Should be interesting.

 

[Guest]

Why not run your pump during the day and then run it again for a few hours at night when you add bleach to circulate it?

 

[Rangeball]

When I get my timer hooked up I do plan to split and run 6 hours during the day during full sun and 6 hours at night.

I tested tonight after allowing the pool to circulate all day. CYA is probably 20, my tube only goes down to 30 and at 30 the black dot was still probably 25% visible.
FC was 3 ppm, same as it was this morning. It wasn't as hot today as it had been, and we had lot's of cloud cover with intermittent bouts of full sun. Also, no swimmers. Hmmm...

I added 1.25 ppm bleach tonight, will test again in the am to get a baseline then shut the pump off.

 

[Rangeball]

Tested this morning. FC is 3.5, CC is 0.

I don't think I'm fighting anything. Rather, a .75 jug of 6% puts 2.5 ppm FC in my pool. The night before, I estimated when I poured "1/2" the bottle in. I laid it on it's side, handle horizontal, and when it stopped pouring out figured that was half. Outsmarted myself and later realized that method would really put in more than half, so in all likely hood I put in less than 1.25 ppm last night.

We've also been experiencing rapid evaporation here. Last night got pretty cool, and overnight loss was noticeable. Some of the FC loss could be from this, right?

Water is crystal clear.

I turned the pump off this morning. Will test again tonight.

 

[Rangeball]

Turned pump on yesterday evening, allowed 5 hours for the water to circulate and mix after sitting in mostly full sun all day, then tested. Got 2.5 ppm FC, 0 CC. Added 1.25 ppm bleach, left pump circulating overnight, retested this morning. Got 3.5 FC with 0 CC.

Short test, only two days, but the results show nearly identical results, especially with a .5 drop test.

Works for me. I'll quit worrying that leaving the water uncirculated in full sun is eating up all my chlorine, and continue to save electricity costs