LC % test?

Lynnster52

Well-known member
Apr 29, 2018
46
Cos Cob CT
Hi - I suspect the remaining case of LC I bought a month ago might have dropped in potency. Is there a ratio of (non-chlorinated) water to LC I need to follow (using the DPD testing method)? I'm science tech-challenged, so if this is an idiotic question, pls be gentle...;)

back story: The newest case of 12.5% LC opened today did not produce the calculated result via PoolMath this am. (pool is crystal clear 0 CC). Just want to know if LC right out of the jug, can be tested!

Tks
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
7,908
Northern NJ
Depends how good you are with measuring small amounts.

What is the largest bucket you have? 5 gallons? 10 gallons?

Set PoolMath to that size pool, tell it you want 10 ppm of FC and it will tell you how many teaspoons to add. Your margin of error in measuring and mixing may be greater then the % difference you are trying to determine .
 

Lynnster52

Well-known member
Apr 29, 2018
46
Cos Cob CT
It's been 3 hrs since I added the LC & I just retested. Pool water is exactly where it was supposed to be after LC addition so for my pool, I need to wait 3 hours for total circulation it seems. Big relief! (I had only waited one hour the first time so while it had more FC than before, it was 2 ppm under.) All good! So the size of the pool & number of jets makes a difference if one needs to retest after adding LC....
 
Last edited:

Donldson

TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
3,843
NW Ohio
We say to test FC 15 minutes later when someone is attempting to diagnose ammonia in the water, not for routine testing. There is rarely a reason to test more than once a day when performing routine chlorination of the pool water.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
7,908
Northern NJ
Enjoy your science experiments.

Sounds to me like you are looking for an unnecessary level of precision in your pool water testing. Close enough is fine. All the tests are given as target ranges. You have a wide range for good FC levels. If you are confident in your testing and FC is low then just pour more in and move on.
 
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Oly

Gold Supporter
Jun 28, 2017
1,098
Fresno, CA
You are better off in my opinion testing your pool water prior to then 1 hour after a chemical application to confirm expected results. Testing a small batch volume increases error as precision becomes essential and any mistake is magnified in the calculation.

Your pool volume estimate is another potential error as is assuming bleach %. If you are reqularly testing your pool water you will catch any inconsistencies before it becomes a problem.
 

Lynnster52

Well-known member
Apr 29, 2018
46
Cos Cob CT
Yes - I totally misread something about retesting after 15 mins thinking that directive was for FC after adding LC! I needed to wait 3 hrs. As far as doing "science experiments", I truly felt the cases of LC might have degraded so it made sense to me to check my pool after adding the LC. That's where I goofed. All is just fine...I'm going up to buy more LC so also wanted to ensure what I have on hand is still good. I got off track when the FC was 2 ppm's lower than calculated - but only due to not allowing enough time for circulation of the pool! I agree I got a bit OCD but the ride to get LC is 2 hrs!
 

IceShadow

Gold Supporter
Jun 8, 2019
1,037
Milwaukee, WI
If you do want to test the potency of your chlorine, you can do this: