Test Results with Low CYA

[SeanH]

Test results from 5/31...

FC=2
PH=7.4
TA=180
CYA=40

These results were from a pool store and agreed with 5 way test strips that I have.

Test results from 6/5
FC=1
TC=1.5
PH=7.6
TA=90
CYA=<20

Over the past week or so, I added a ton of bleach (based on the calculator) to clear up green algee.

3 days ago my PH was reading < 6.8 so over the course of the last 3 days I have added around 9 lbs of Borax and the PH is now 7.6.

I have a tri-chlor tabs in an inline chlorinator.

Other than that I've done nothing but brush and vacuum. No one has used the pool and there hasn't been any water loss.

I first tested the CYA with the "black dot vial" test on 6/2. The water was perfectly clear and I could clearly see the black dot. When I tested it today, the water was a little cloudier when viewing the dot, so it looks like I'm getting CYA back in via the tri-chlor tabs.

I understand all my results except the CYA. How could the CYA have dropped from 40 to < 20 that quick with no water loss? That's the only real way to lose significant amounts of CYA correct?

I'm a little confused...

Sean

 

[JohnT]

CYA tests read high when the water is cloudy from algae. Once it clears, your reading will go down.

 

[SeanH]

CYA tests read high when the water is cloudy from algae. Once it clears, your reading will go down.

Would that affect test strips?

I'm not sure how Leslies test for CYA so I don't know if it had an affect there or not.

I guess at this point it really doesn't matter. I need to get the CYA up some. I'm just being cautious because I don't want to get it too high.

Sean

 

[JohnT]

CYA tests read high when the water is cloudy from algae. Once it clears, your reading will go down.

Would that affect test strips?

I'd assume not, but I don't know for sure.

 

[akelley]

I've got a similar situation where I've got little to no CYA and I'm using trichlor pucks in both a feeder and floater. Everytime I do the "dot" test, I can clearly see the dot when the vile is full so I have less than 20 CYA reading, if not any. Like SeanH is asking, where is my CYA going? At this level does it make sense to add CYA so I'm not potentially wasting my chlorine?

 

[Rangeball]

Isn't there a school of thought that certain organics eat cya? I know it's been discussed as a potential explanation for loss of CYA after closing for the winter and opening in the spring, but haven't seen anything related to it disappearing that fast during normal operation.

Another consideration, how old are your CYA strips? I'd be tempted to make sure I ran the dot test correctly now that the water's cleared up and go by it. Also, if you plan to continue using the tri-chlor tabs I wouldn't worry about adding any, just keep an eye on it and stop using the pucks when you hit your personal threshold.

 

[chem geek]

It's soil bacteria that can get into the pool and over the winter when a pool is "let go" without maintenance of chlorine levels, the bacteria can thrive and consume CYA turning it into ammonia (the metabolic pathway is shown in this link). Every 10 ppm CYA turns into 3.3 ppm ammonia and would require in the neighborhood of 30 ppm FC to get rid of (some ammonia will outgas from the water as it is a little volatile so it isn't always found over the winter even when the CYA has dropped).

However, when Free Chlorine (FC) levels are maintained, the bacteria should not survive. It is possible for high chlorine levels to slowly break down CYA especially at higher pH, but this is a very slow process at the normal levels of chlorine found in pools. Splash-out, backwashing and other sources of dilution are more likely. Of course, it's always possible there's some other mechanism we're not yet aware of.

Richard

 

[SeanH]

Isn't there a school of thought that certain organics eat cya? I know it's been discussed as a potential explanation for loss of CYA after closing for the winter and opening in the spring, but haven't seen anything related to it disappearing that fast during normal operation.

Another consideration, how old are your CYA strips? I'd be tempted to make sure I ran the dot test correctly now that the water's cleared up and go by it. Also, if you plan to continue using the tri-chlor tabs I wouldn't worry about adding any, just keep an eye on it and stop using the pucks when you hit your personal threshold.

The test strips were from last season. They had the same reading (40) as when I had the water tested at the pool store. I guess both tests could have been flawed.

I'm out of tri-chlor tabs, so I either need to get more, or get some CYA. I'm going to get the pool store to test again and see if the results are the same as what I'm testing.

The most logical answer (based on what I've read here) is that the tests from 5/31 were not accurate.

Sean

 

[SeanH]

I had a water test done tonight at the pool store and they confirmed what I've been seeing. CYA=0.

The girl made a comment about the FC level being a little high to which I responded....yeah, that's from all the bleach I've been putting in. The look on her face was priceles!!!

They sold me a bucket of CYA. I also picked up a FAS/DPD service test kit while I was there.

My question is how to add the CYA. The directions say to mix with warm water and add to the skimmer. My skimmer line is broken so it's shut off right now. I have someone coming out tomorrow (hopefully) to fix it. I've read on here about putting it in a sock and in the skimmer, or in front of a return.

What's the best way to add CYA? It looks like I need to add around 8 lbs. Should it be added slowly over time or in one shot?

Sean

 

[JasonLion]

Add about 2/3rds of the amount of CYA you calculate you need, wait a week and retest.

The simplest thing is to pour it into a skimmer and then remember not to backwash/clean the filter for a week. If you don't have a skimmer then put the CYA in a sock and hang it in front of a return.

 

[SeanH]

Add about 2/3rds of the amount of CYA you calculate you need, wait a week and retest.

The simplest thing is to pour it into a skimmer and the remember not to backwash/clean the filter for a week. If you don't have a skimmer then put the CYA in a sock and hang it in front of a return.

Thanks for the info. My skimmer should be fixed today or tomorrow so I think I'll wait and put it in then.

Sean