Aeration eating chlorine?

[woodyp]

Ok folks, it was a classic burner here in Texas today. 98 temp with 104 or better heat index. Ran the (cutsie) flower aerator that screws into the return all day to help lower water temps so it wasn't a hot tub tonite. Might have to strap an ice bucket on the old pool rover! I know aeration has a tendency to raise PH. Does it also have any effect on burning off more chlorine as opposed to not using it?
My FC dropped from 7.5 last nite to 3 tonite. Just jacked it back up to 8 for safety. CYA is 50 and Ph is on target.
Just increased pump run time from 10 to 12 hours daily tonite.

Thanks guys (and gals).

 

[chem geek]

Yes, the aeration could cause more outgassing of chlorine. It's normally fairly slow, but a lot of aeration can accelerate it. Recall that keeping a bucket of chlorinated tap water open to the air overnight usually reduced the chlorine level in it (assuming chlorine, not the more recent monochloramine added to many water supplies today), but such water didn't have CYA which reduces the rate of chlorine outgassing significantly.

Your overall chlorine demand may also be higher due to the higher water temperature. However, with no sunlight even 90ºF pool water would probably still have < 1 ppm FC chlorine demand over 24 hours so less overnight. So the increased drop is likely to be from the aeration, though clearly most of the drop is still due to sunlight. You didn't say what your normal loss is, but if it's 3 ppm FC then the extra 1.5 ppm FC drop could certainly be from the aeration.

 

[woodyp]

Normal chlorine drop thus far (I''ve only had the pool for a month) has been on average 3ppm. That was before the heat and temps got to where it is now! It was also before I decided to connect the aerator and try it to see how much it might lower the pool temp. Pool temp just got to 92 or 93 degrees here. Thanks for the in depth response.