Does chlorine really get used up that fast?

[surfhawaii]

FC in the morning was 7, twelve hours later it's at 0. Now, CYA level is still at zero because I just added it a few days ago and it's slowly dissolving thru socks and I think you said it takes a week or so to register so maybe it's not helping to keep chlorine in the water (and it was a fairly sunny day), but can it drop that much in 12 hours?

 

[257WbyMag]

It can drop that much in a couple of hours. CYA is that important.

 

[frustratedpoolmom]

While it takes a week to fully register on tests - it should start to work within the first 24-48 hours. I'm guessing there is something lurking consuming the chlorine as well. The best way to rule out sunlight is to dose the chlorine in the evening when the sun is off the pool and see what kind of overnight drop you have. If it drops more than 1ppm then it's not from the sun. KWIM?

 

[dmanb2b]

Like FPM, you may have a combo of still too low CYA and possible organics...as she suggested the overnight FC loss test would be your best bet. Here is a link to the instructions

pool-school/overnight_fc_test

 

[surfhawaii]

Ok. Will do. Also, got a few more questions:

Yesterday I cut the grass and weedwhacked around the pool perimeter. Even though I use a grass catcher and try to blow grass away from the pool, the trade winds blow grass trimmings into pool and there is no way from preventing almost the entire surface of the pool from being lightly covered with grass. I try to skim off as much as I can but know I don't get it all. Could this be contributing or no big deal?

Is combined chlorine an issue, should I be measuring/tracking? I don't see much reference to it. It's been zero.

I see lots of references in pool school to shocking. And understand that could be bleach but when you say 'shock' it and/or 'continue shocking', what exactly does that mean with regard to how much to add? Or is there a better chemical to use?

As always, thanks for your prompt responses.

 

[frustratedpoolmom]

Bleach a.k.a. liquid chlorine is the preferred product for shocking. In some cases, dichlor granules or cal-hypo granules can be used to shock.

Use the Pool Calculator to figure out amounts of each chem to add - if you need help on learning to use it, just holler.

Combined Chloramines, CC's are important in that if they get above .5 you usually should shock the pool. Sometimes sunlight helps rid the pool of them but if they get much higher than .5 that's a sign something organic is happening.

I wouldn't worry about the grass.

 

[chem geek]

FC in the morning was 7, twelve hours later it's at 0.

If there is no CYA in the water, then at a pH of 7.5 chlorine in an average depth pool will drop in half every hour in direct noontime sun. 12 hours is roughly equivalent to around 8 or so hours of direct noontime sunlight so 7 ppm FC would get to 7*(0.5)⁸ = 0.03 ppm which would register as zero on a test kit. Even after 4 hours near noontime, it would go from 7 ppm FC to around 0.4 ppm.