Chlorine / CYA Chart

Philo

Well-known member
Oct 8, 2015
944
San Diego, Ca.
If it is safe to swim in a pool up to the SHOCK level of chlorine, why doesn't the chart read: :confused:
CYA...............50
Target FC.......4-19
Shock Level....20
 

BuckeyeChris

Well-known member
Jan 28, 2014
824
Buckeye AZ
You only add enough chlorine to keep your pool sanitized and algae free throughout the day. If your minimum is 4, and you lose say 3 ppm per day, you only need to start the day at 7. for example. The further you skew the CYA/FC ratio toward FC, the more of that chlorine is not bound to cya. It will burn off faster. So by being way higher than is needed, you are wasting chlorine and money.
 

Philo

Well-known member
Oct 8, 2015
944
San Diego, Ca.
That's what I thought also, but in my actual experience, the drop of FC daily is amazingly consistent of -1.5 FC per day. Dropping from 19 to 4 in a week.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
That's not usual. Usually during the day one loses more chlorine at higher FC levels, CYA held constant. The loss is roughly a percentage loss. This is why the daytime losses when doing a SLAM are much higher than at normal FC/CYA levels. For your 19 to 4 in a week (which by the way would be an average of (19-4)/7 = 2.1 ppm FC per day) it may be a 20% loss per day such that you go 19 --> 15.2 --> 12.2 --> 9.7 --> 7.8 --> 6.2 --> 5.0 --> 4.0 where the initial loss is closer to 4 and the last loss is closer to 1. So are you saying that when it was at 19 ppm FC you did an accurate FAS-DPD test at that time and then 24 hours later and found it to be at 17.5?
 

Philo

Well-known member
Oct 8, 2015
944
San Diego, Ca.
Thanks for responding Richard.

Here are my exact FC----FAS-DPD readings:

Monday 8.5 (added 3 gal of 10% Chlorine)
Tuesday 17.5
Wednesday 15.5
Thursday 14.0
Friday 11.5
Saturday 10.5
Sunday 9.5
Monday 9.0
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
So there is +/- 0.5 ppm for the 10 ml sample size it looks you are using, but it's clearly using up more chlorine initially at around 2 ppm FC dropping to 1 ppm or less at the end. The 2.5 ppm between Thursday and Friday is a blip but may really be 2 ppm and perhaps was a sunnier day. I thought you said that it dropped from 19 to 4 over a week -- the above would be from 8.5+10 = 18.5 ppm down to 9.0 ppm. Your chlorinating liquid might actually be more than 10% or your pool volume smaller than 30,000 gallons. With your numbers the deltas each day are as follows: 1.0 2.0 1.5 2.5 1.5 1.0 0.5
 
Thread Status
Hello , This is an inactive thread. Any new postings here are unlikely to be seen or responded to by other members. You will get much more visibility by Starting A New Thread