Using more chlorine than past years...not sure why

[jmbuys]

Wondering if I'm missing something. Follow TFP FC/CYA methods closely the last several years and it works great! This season (pool has been open about 5 weeks) I notice that the pool is using about 25% more chlorine than the past several years and I have no idea why.

FC: 7
CC: 0
pH: 7.6
TA: 40
CYA: 40

Since I'v managed this pool (several years) once balanced after opening, 1 gallon of liq chlorine raised FC by 2, which on most sunny days was exactly what was used up over 24 hours (less on cloudy days etc). The last several years I've kept CYA at 40 so that hasn't changed. This year a gallon still raises FC by 2, however on sunny days I find this year that FC is reduced almost by 3 (over a week it's more like 2.7). I've tried Cal Hypo as chlorine source as a test as well...same thing.

No algae problem I'm just adding an extra 1/4 gallon to match demand. No extra bather demand this season, all my other numbers are consistent w/ past years. Water nice and clear. Other than some iron in the water from my fill water...no other problems.

Am I missing something/not testing for something? Other than it costing me a little more for sanitation it's not a huge deal but just not sure if it's something to keep investigating. Thanks

 

[Jimrahbe]

No algae problem

jm,

How would you know?? Algae can consume FC long before you ever visually see it..

I suggest that you run on Overnight Chlorine Loss Test or OCLT.. Just to make sure.

Overnight Chlorine Loss Test

The other option would be your CYA.. When I run into this issue, it is almost always because my CYA is lower than I thought.. Mainly because I don't test my CYA as often as I should...

Thanks,

Jim R.

 

[jmbuys]

Good idea...will test that tonight. I did it after I opened the pool but that was 5 weeks ago. Feel good about the CYA number that has been consistent since balancing the stabilizer after opening.

 

[Sunnydaze]

How old are your test reagents? Maybe it's the testing that has changed slightly.

 

[jmbuys]

Hmmm different ages but the 870/871 I restocked end of last year so 9-10 months.

 

[jmbuys]

It did pass OCLT last night...so no unusual activity/FC loss overnight. Double checked cya...still 40. If any other ideas would love to hear otherwise will just consider it a slight annoyance to deal w/ this season. Thx

 

[Newdude]

What's the date code on the bleach ? Even if it's fresh, it could have sat in the parking lot behind the store for some time before making it to the shelves.

Anytime you wonder, test 20 mins after adding to ensure you hit your target.

 

[borjis]

You might consider bumping your cya to 50.
I had mine at 30 and it just wasn't enough. Bumping it to 50, my chlorine levels lasts longer as a result.

 

[duraleigh]

In years past, was your CYA always 40?

Like borjis, I would suggest 50 or maybe even 60 for your climate.

 

[jmbuys]

Yes CYA has been maintained at 40 every year-it usually works nicely for me....I can def bump it up to 50 to see if it helps -still makes me wonder why the change in FC utilization at the 40. The liquid chlorine (and the cal hypo trial) both raised FC by 2, 30 min after application as it has in past years.

 

[Newdude]

Are you testing the CYA with overhead sun? That's about the only way to completely botch the subjective test.

FWIW, several of us saw high UV loss early this year. My FC was tanking at 30/40 CYA which should have been plenty for early spring in the northeast.

 

[poolshrinker]

Wondering if I'm missing something. Follow TFP FC/CYA methods closely the last several years and it works great! This season (pool has been open about 5 weeks) I notice that the pool is using about 25% more chlorine than the past several years and I have no idea why.

FC: 7
CC: 0
pH: 7.6
TA: 40
CYA: 40

Since I'v managed this pool (several years) once balanced after opening, 1 gallon of liq chlorine raised FC by 2, which on most sunny days was exactly what was used up over 24 hours (less on cloudy days etc). The last several years I've kept CYA at 40 so that hasn't changed. This year a gallon still raises FC by 2, however on sunny days I find this year that FC is reduced almost by 3 (over a week it's more like 2.7). I've tried Cal Hypo as chlorine source as a test as well...same thing.

No algae problem I'm just adding an extra 1/4 gallon to match demand. No extra bather demand this season, all my other numbers are consistent w/ past years. Water nice and clear. Other than some iron in the water from my fill water...no other problems.

Am I missing something/not testing for something? Other than it costing me a little more for sanitation it's not a huge deal but just not sure if it's something to keep investigating. Thanks

i don't have answers but am surprised by the amount of chlorine you are using regularly. I can't see your pool size from your phone. My 17,000 gallon pool uses 1 gallon liquid chlorine maybe once per week, but it's not used every day and we're pretty good about keeping the solar cover on when not being used.

 

[poollifeguard]

Sounds frustrating! I Had a similar issue last summer. Turned out my pool was getting more direct sunlight than usual due to a tree being cut down. Maybe check if anything's changed in your pool's environment? More sun exposure can definitely increase chlorine demand.

 

[jmbuys]

Thanks guys. Only environmental thing is it's been a little warmer in the Northeast, but water temp about 78 so nothing strange there. Also been windy and I have lots of pine trees so more material to pull out than most years but I'm pretty good about it. Yup the CYA can be finicky to test but the 40 lines up w/ the amount of stabilizer I added (from 0 at pool opening).

It's a little over 25K gallon pool, not using solar cover, but still I'm amazed you only need a gallon a week poolshrinker?? what is your cya?

 

[poolshrinker]

CYA is 40. but we don't swim everyday. i think a gallon a week is just minimal baseline, i find that if 4 teenage boys are swimming for a few hours half a gallon of chlorine is necessary and sufficient to get back to target!