High Chlorine consumption?

[PoolStored]

Pool stats in my signature.

Had High CYA (90). Partial Refill, Slammed successfully. Been doing 12 hour cycles of MA/Aerating and have reduced my TA from 140 to 70. Works good.

However, during this time, the pool has been uncovered. It gets a lot of sun during the day and has been warm 80s outside. Pool has been crystal clear, I can read head or tails on a quarter on the bottom. Continued brushing and no slimy feel on walls etc.

Numbers:
pH going from 7.0 (MA addition) -> 7.4 (After aerating 12 hours).
FC 4-4.5 (sundown) -> 7.0-7.5 (morning, after chlorine pump runs).
CC = .1/.2
TA now 70
CH 375
CYA 42 on the test, treated slam and target FC as though the pool is a 50 (as members instructed).

My question:
What is causing consumption of 140-160 ounces of 10% bleach daily? Seems like a gallon and 1/2 per day is a lot.
Potential Answers:
1) Not using the solar cover?
2) Hated CYA so much that I drove it to 40, when it really should be 50, or 60? (one of the threads from Chem Geek (Chlorine Usage at different CYA levels indicated that (I'm extrapolating) 7 ppm FC at 40 ppm CYA loses 0.6*7 = 4.2 ppm) I'm losing about 3ppm. If I recalc using CYA 50, then 0.5*7 = 3.5). Closer, but I'm not losing that much.
3) Does aerating consume Chlorine? Most reference I see say no.
4) Does lowering the pH to 7.0 consume more Chlorine? Most things I've found here say no.
5) Should I really target 3 FC at night and 6 FC with pump overnight (midrange FC target at 40 CYA from CYA/FC chart) instead of 4 and 7? JasonLion indicated in the same reference thread: "a higher starting FC level means more chlorine lost to sunlight (all else remaining constant). These are really sunny hot days, so I suppose this is going to be my upper limit (140-160) and likely will come down on more cloudy cool days.
6) Other losses not related to Sunlight? Tall Trees around the pool and lots of vegetation to the we of the pool and dominate winds from the west is raising the Chlorine need with pollen etc?
7) Slam didn't actually finish even though I met all 3 criteria, or my testing was faulty?
6) Other thoughts?

Just seeing what I can do to reduce the usage. Thanks for the help!

 

[proavia]

2-4 ppm of FC loss is normal in summer. You have a 36,000 gallon pool - more water takes more chlorine to attain a specific FC level.

 

[Panzer]

A combination of factors..
1) Not using the solar cover will consume more chlorine than if you have it covered. While the CYA will help maintain the chlorine level, the sun will inevitably burn-off some.
3) Aeration will consume some Chlorine. Not near as much as losses to sun and organics but, aeration will contribute to Chlorine loss.
6) If there is a high probability that you're introducing materials into the pool... pollen, etc, You should expect that it will lower your FC as well.

A solar cover can help with (2) of those.
As Proavia stated, with a pool as large as yours... the volume of everything is going to be much higher. If you get more concentrated Chlorine source you can lower the volume you need but, you'd need to figure a cost/benefit analysis for yourself.
Respectfully,

 

[MITBeta]

Your chlorine usage of 3ppm/day is right in the middle of normal.

But... you're flirting with issues by allowing FC to fall to the absolute minimum. This leaves no margin of error for unexpected organics in the water. Based on the FC/CYA Levels I would be targeting the high end of target, or even a point higher so that when you lose 3ppm it's still in the target range.

 

[PoolStored]

Your chlorine usage of 3ppm/day is right in the middle of normal.

But... you're flirting with issues by allowing FC to fall to the absolute minimum. This leaves no margin of error for unexpected organics in the water. Based on the FC/CYA Levels I would be targeting the high end of target, or even a point higher so that when you lose 3ppm it's still in the target range.

Great suggestion! Thanks.