disappearing CYA

[wweissborn]

I was testing my water last week and I had a cya of about 60 (maybe a little higher). We had some rain so I tested chloring and CYA yesterday. Chlorine and CYA are now non-existent. I expected the chlorine to disappear because of the rain but I've always been told that I'd have to basically drain the pool and add fresh water to get a 0 cya reading. It didn't rain that much last week and I didn't drain the pool. So how does it get "used up"?

Bill W

 

[FattyLumpkin]

CYA issues can often be attributed to testing error. But a 60+ point loss to a level of zero seems to indicate something more sinister is going on -- possibly ammonia, but my understanding is that that occurs more often over the winter. Can you post a full set of numbers? I'm sure a true expert will chime in as well.

 

[mknauss]

You are correct, to lose that much CYA in your water that fast you would need to have drained your pool.

Typically means a testing error. Was the water circulating when you sampled? Did you get the sample from a foot or so below surface? Did you do the test with the same lighting you normally do it?

Take care.

 

[wweissborn]

Sorry, let me clarify. I tested CYA about 7-10 days ago. It was done according to the "disappearing dot trick". It was then basically zero, again according to the disappearing dot, when I tested this past Sunday. In between we had a lot of rain and an algae-bloom. Very little chlorine was added apparently (that's what happens when you let your grandkids take over maint. I guess). Sunday the FC was also zero and ph was off scale (probably close to 9 if I had to guess).

I've added a little CYA granules yesterday, via sock in skimmer, and this morning the CYA is between 20 and 30. FC was just barely registering so maybe 1. Out of chems for pH and Alkalinity but will post a full set of numbers this evening/tomorrow.

Hope that helps

 

[domct203]

Sorry, let me clarify. I tested CYA about 7-10 days ago. It was done according to the "disappearing dot trick". It was then basically zero, again according to the disappearing dot, when I tested this past Sunday. In between we had a lot of rain and an algae-bloom. Very little chlorine was added apparently (that's what happens when you let your grandkids take over maint. I guess). Sunday the FC was also zero and ph was off scale (probably close to 9 if I had to guess).

I've added a little CYA granules yesterday, via sock in skimmer, and this morning the CYA is between 20 and 30. FC was just barely registering so maybe 1. Out of chems for pH and Alkalinity but will post a full set of numbers this evening/tomorrow.

Hope that helps

Just a reminder, but the CYA test needs to be done outdoors on a bright sunny day, back to the sun, and reading the test vial in your shadow at about waist level.

https://www.troublefreepool.com/content/220-CYA

As mentioned, a drop in CYA of 60ppm over the course of a week is not normal. If the CYA was converted to ammonia by bacteria, you will have a very difficult time holding FC, and it will disappear just about as fast as you add it. Each addition of CYA will just continue to covert to ammonia until you kill the bacteria with a proper SLAM.

Next time you check FC, dose enough chlorine to reach 10ppm. Check FC in 10 minutes, if it is less than half (5ppm) redose up to 10ppm and repeat this until you can get the FC to hold. Once FC is holding you can add CYA to reach 30ppm and SLAM the pool.

 

[peirek]

Just a reminder, but the CYA test needs to be done outdoors on a bright sunny day, back to the sun, and reading the test vial in your shadow at about waist level.

https://www.troublefreepool.com/content/220-CYA

As mentioned, a drop in CYA of 60ppm over the course of a week is not normal. If the CYA was converted to ammonia by bacteria, you will have a very difficult time holding FC, and it will disappear just about as fast as you add it. Each addition of CYA will just continue to covert to ammonia until you kill the bacteria with a proper SLAM.

Next time you check FC, dose enough chlorine to reach 10ppm. Check FC in 10 minutes, if it is less than half (5ppm) redose up to 10ppm and repeat this until you can get the FC to hold. Once FC is holding you can add CYA to reach 30ppm and SLAM the pool.

Should he get his pH in check before executing the SLAM? pH of about 9!!

 

[domct203]

Still waiting on a new set of test results ......

 

[dschlic1]

I have had experience with some kind of white water borne organism that will eat CYA and laugh at normal levels of FC. Try this: at night turn on your pool light. Look into the pool at right angle to the light beam. If you can see the beam then you probably have what I had. If so do not add CYA as that will only make things worse. Do a SLAM, using max level of FC. This stuff is really hard to get rid of.

 

[peirek]

I have had experience with some kind of white water borne organism that will eat CYA and laugh at normal levels of FC. Try this: at night turn on your pool light. Look into the pool at right angle to the light beam. If you can see the beam then you probably have what I had. If so do not add CYA as that will only make things worse. Do a SLAM, using max level of FC. This stuff is really hard to get rid of.

Maybe you can bottle that and sell it to reduce CYA?

 

[wweissborn]

For giggles this morning I checked the CYA. I must have misread the reading or was in too bright a light the first time because today the CYA was 50. FC was around 5 and pH was 7.8 I added some more bleach this evening and will check in the morning to see what my levels are.

BUT it appears the problem was basically a PEBCAC or ID10T error.