How much chlorine does your pool use? Corollary: what drives loss of chlorine

sws1

Well-known member
Aug 13, 2010
55
Neptune City, NJ
I shocked my pool a few days ago, and have been watching how much the FC drops during the day. My CCs are pretty much at zero now, so I'd think FC would drop during the day as a result of sun, but not quite as much as I'm seeing.

Over the past few days, FC dropped 24 to 15. Then 15 to about 7ish. This is with a CYA of 50. Hence, that means I'm using a gallon of liquid chlorine per day (or more) for a 29k gallon pool. I found an old thread somewhere is it sounded like others were using FAR less than I am.

My pool is direct sun from about 9-6. So that'll take some FC. But it still seems to drop faster than I would think. (especially with no swimmers)

What else would drop the FC? Could the excessive droppings from the trees be a cause? (I'm out there every hour or so skimming all sorts of "thingies" that are coming off the spring trees.)
 

ragart

Active member
Jul 11, 2018
26
Philadelphia, PA
I shocked my pool a few days ago, and have been watching how much the FC drops during the day. My CCs are pretty much at zero now, so I'd think FC would drop during the day as a result of sun, but not quite as much as I'm seeing.

Over the past few days, FC dropped 24 to 15. Then 15 to about 7ish. This is with a CYA of 50. Hence, that means I'm using a gallon of liquid chlorine per day (or more) for a 29k gallon pool. I found an old thread somewhere is it sounded like others were using FAR less than I am.

My pool is direct sun from about 9-6. So that'll take some FC. But it still seems to drop faster than I would think. (especially with no swimmers)

What else would drop the FC? Could the excessive droppings from the trees be a cause? (I'm out there every hour or so skimming all sorts of "thingies" that are coming off the spring trees.)
I'm having a similar issue. Close to zero CC. I add in 5ppm FC and it is gone within a few hours. It was holding chlorine well until yesterday when we had some swimmers (4) and a lot of floats in the pool. Since then, the FC is gobbled up VERY quickly.
 

sws1

Well-known member
Aug 13, 2010
55
Neptune City, NJ
UV from the sun will consume 2-4 ppm FC per day. As long as you have appropriate level of CYA. 30-50 ppm CYA (depending on climate) is sufficient for non-SWCG pools.

Both of your pools act like they have algae. Do a Overnight Chlorine Loss Test tonight.
I did it the other day, when the FC was at 25 and it was at 25 in the morning. I think I did it the next night too with same result, but I've done so many tests, I may have forgotten. I will try again.
50 CYA, by the way.

(I have a new batch of test chemicals arriving shortly, so maybe I'll get better data with fresh stuff.)
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
29,552
Laughlin, NV
If your CYA is 50, you should not be going above a 20 ppm FC level. Your vinyl liner will potentially be damaged by the elevated FC.
 

sws1

Well-known member
Aug 13, 2010
55
Neptune City, NJ
Well, got my new chemicals.

But unlike a few days ago, when I didn't have ANY CC after slamming. Now I'm showing some again. THIS, despite the water being absolutely crystal clear. 8.5' looks like 3'.

If swimmers and algae can cause CCs to form, wouldn't debris from trees also generate CCs if they sat in the pool? What about stuff that was sucked into the filter? Could tree debris/dead algae that's in the filter be generating CCs?

Might be another week or so before the debris stop dropping stuff.