CYA levels lowered by chlonine????

oarmas25

New member
May 17, 2012
1
I am working on getting my pool swim-able and 2 weeks ago when I got the water tested at a leslie's my CYA was at 60 and the chlonine level was low. Recently about a week ago I noticed some algae so I added 5lbs of pool-time shock plus to kill all the algae and hopefully have enough chlorine to last a week. About 5 days later i checked the chlorine and it was at 0 so i started wondering if the CYA was too high and causing the chlorine not to work properly. After reading many websites i am convinced not to use pool time shock plus because it will increase the CYA levels and the safest way would be to use liquid chlorine. So i added about a gallon of liquid chlorine last night and my chlorine level today is about 8ppm too high and CYA at 25 according to leslies.

Everything i have read in the past points out that CYA cannot be lowered unless is drained partially/completely depending on the LEVELS. Now my concern is how come leslies test shows that my CYA is at 25 when two weeks ago was about 60. Is this possible?

The pool looks great but I dont know how long the chlorine will last in the water. I always thought chlorine should last about a week. I will test the water daily to see how fast is being consumed. Its been about 90 degrees and the pool is in direct sun almost all day so I know that plays a part in the chlorine.

I feel like I always have algae problems so I just starting using leslies pool perfect plus phos-free to hopefully lower the levels of phosphate in pool and control algae.

I was told by leslies to add conditioner in my pool to bring the levels up but I am concerned this will actually cause a problem.

What should I do????
 

PSW

TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Feb 13, 2012
728
Phoenix, AZ
oarmas25 said:
Everything i have read in the past points out that CYA cannot be lowered unless is drained partially/completely depending on the LEVELS. Now my concern is how come leslies test shows that my CYA is at 25 when two weeks ago was about 60. Is this possible?
You are correct (that CYA will only be lowered by replacing water). And this goes to show how inaccurate pool store test results can be. It would be wise to get your own test kit and test your water on your own.

oarmas25 said:
The pool looks great but I dont know how long the chlorine will last in the water. I always thought chlorine should last about a week. I will test the water daily to see how fast is being consumed. Its been about 90 degrees and the pool is in direct sun almost all day so I know that plays a part in the chlorine.
Chlorine consumption is based on several factors..algae presence, CYA level, and sunlight.

oarmas25 said:
I was told by leslies to add conditioner in my pool to bring the levels up but I am concerned this will actually cause a problem.
Again, your intuition is correct. You should not add any more conditioner until you KNOW what your CYA is.
 

Isaac-1

TFP Expert
LifeTime Supporter
May 10, 2010
6,711
SW Louisiana
Edited to remove conflicting information and prevent confusion to newbie. Butterfly A much higher chance is one or both of the tests were wrong. This is part of why we so strongly suggest getting a good test kit like the Taylor K-2006 or the TFTestkits TF-100 (I use the TF-100), pool store testing is notoriously wrong. I just had some water tested for iron due to a rust/iron shavings contamination issue last week (I don't have an iron test since it is not normally an issue in my pool), and the pool store numbers were wrong more than right (they showed my CYA at 10, really at 25-30, CH at 80, really 160, and TA at 110 or so and really around 60-70).

Ike
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
11,762
Houston, Texas
Hi, welcome to TFP! Pool store testing is notorious for being inaccurate, especially for CYA. The most common CYA test has a +/- 10ppm accuracy, meaning if you get a CYA result of 50 it could actually be 40 or 60. Part of the reason for the error is reading the test depends on noting the point when a black dot is no longer visible at the bottom of a test cylinder while pouring in the test solution. Lighting conditions and eye sight issues can effect how the test is read. Some stores will use a computer to run the CYA test, but the computer must be re-calibrated frequently to maintain accuracy. Plus the test is only as reliable as the individual conducting it. I would have another sample tested, preferably at another store and see if the result is anywhere near the previous one.

This brings me to my next item. In order to take control of your pool you should have a high quality FAS-DPD test kit such as the TF 100. It will allow you to test very high levels of chlorine needed to complete the shock process and performing your own tests allows you to have more consistent results. You can test the pool every day or two and dose the pool as needed to keep it balanced.

Now, chlorine will continually deplete as it oxidizes organic matter in the water. How quickly it depletes depends upon how much organic matter there is, and how much UV exposure the chlorine has. The CYA provides protection from the sun's UV rays. Too much CYA protects the chlorine so well it is rendered ineffective and allows algae to grow unchecked. CYA only "disappears" on its own when it is consumed by bacteria and that usually only happens over winter or when certain fertilizers are introduced into the pool. The whole "add shock once a week" thing is the expectation that a bag of shock will raise the pool to shock level (10ppm in theory) and it will take about a week for the chlorine to deplete to between 1-3 ppm. While that is standard pool industry recommendation, it does not take into account any variables such as bather load, or CYA levels.

A properly chlorinated pool will not grow algae no matter how high the phosphate level gets. Chlorine will need to be replenished every day or two to keep it at recommended levels. Read through pool school and take a look at the pool calculator and you will learn more about caring for your pool.
 

Suziqzer

TFP Expert
Sep 21, 2009
914
Greentown, IN
Wow.. these people are fast! I was responding to your post and went to see if you had any responses yet and see several already. :)

Welcome to the forum! This place is great and I'm thankful to have found it in time to start out on BBB. With their comments, and the pool school section, you will be well on your way to a much more beautiful and clear pool with little effort, and likely much less cost than you are used to. And, I concur... order a test kit... Pronto!!

One thing I would like to add to their comments. You could add your pool specs to your signature line (go to user control panel, then profile, then edit signature) so that those trying to help you can have a better understanding of your pool size, make up- is it vinyl, plaster, etc.
 

keastman

Well-known member
May 9, 2008
51
NE Florida
Interesting timing on this post. I just went through something similar. I have a K2006 test kit and test at home. My CYA was 50-55 (repeated tests) before I started shocking the pool for a suspected mustard algae problem, that started after bringing my Cl levels down from 20 after shocking this spring. The algae started with a cl of 12 or so, despite holding chlorine overnight and having CC of less than 0.5. I think it was being harbored in some in floor cleaning runs that were stagnant which I have since corrected. So I ran the chlorine up to 25-30 for a week and it looks good again while the Cl level is dropping. I tested CYA again yesterday and now it is between 30-40. I repeated it today and it's still the same. So, I was wondering if the high Cl levels burned some of it off. There has been no rain or water added to the pool in that time frame.
What ever caused the drop, I'm going to add more to get it back up to levels appropriate for my swg and hope the algae keeps at bay.