Pucks are not raising my CYA

[Rocket J Squirrel]

My refurbished IG gunite/plaster pool was refilled with tap water at the end of April. At that time, the PB tossed in a starting dose of CYA stabilizer. CYA started out at 30.

I've been using a hybrid approach of 10% liquid plus trichlor 3" pucks to add Cl, mostly because I bought the pucks just before I learned about TFP. When the FC needs a goose, I dump in the liquid. The rest of the time, the pucks sit in a floater. I figured once my CYA rose to 40, I'd quit using the pucks routinely.

It is now late July, and my CYA is still 30.

I believe I'm doing the test correctly. My test equipment is clean, my reagent is fresh, and there's no ambiguity with the black dot. Back to sun, waist level, etc. At 40, the dot is visible. At 30, it's gone.

How is this possible? Everything I read here says pucks will cause CYA to rapidly rise. In this case, I want the CYA to rise.

Today's test results follow. After this reading, I added 3 more pucks to the floater.

FC 2.0
CC 0.5
pH 7.4
TA 100
CH 330
CYA 30

 

[pabeader]

How many pucks have you used so far?

 

[Rocket J Squirrel]

That's a very good question. I have about half of my 20 lb. bucket left, so I'd say 10 lbs.

 

[PoolFool.]

PoolMath calculator says that for a 40K pool it will take 100 ounces of trichlor to raise your CYA by 10 ppm.
So figure out how many you have used (hopefully from just one bucket) and see where you should be.
That would also lower your ph by 0.9, (well at my borate and tA levels anyway) have you also been having to boost your ph?

Also did you have 2 independent sources confirm your CYA was actually 30 when you started? The CYA graduations seem to become very logarithmic at the low end of CYA, which would theoretically make it easier to be precise. But my test kit stops at 30 ppm, nothing below that is tstable with my Taylor kit.

 

[getreal720]

10 pounds of trichlor pucks should raise your CYA by 17ppm in your 40,000 gallon pool.

Maybe your pool just needs a bit more time for the CYA in the pucks to "take effect". The levels can take up to a week to respond in some cases. I'm not sure what the norm is for a trichlor puck as far as how quickly the CYA increase shows up on tests.

 

[Rocket J Squirrel]

Thanks for the replies, and for doing the math I should have figured out myself.

No one verified my initial reading of 30. Just me staring at the dot. So it's possible my initial readings were inaccurate due to my lack of experience staring at dots at that time.

I have never had to raise my pH. I have to lower it occasionally. Fresh plaster causes the pH to rise. It's now pretty stable and easy to keep in the middle 7s.

Regarding the time it takes for CYA to appear on the test, I hope I don't test one day and find it's all appeared at once and my CYA is suddenly too high.

I'm asking about this mostly from curiosity. My pool water is perfectly clear and pretty well balanced, so it's not a huge concern.

 

[benm2010]

You have used 10 lbs since April, correct? If so I believe CYA naturally degrades at about 5 ppm per month so over 3 months (May, June, July) you would have lost about 15 ppm and added 17 ppm... so your CYA should essentially be the same. Everything appears normal to me.

 

[Bama Rambler]

CYA doesn't degrade nearly that fast, more like 5ppm per year.

Do you know how much CYA the PB dumped in the pool to start with? If you don't, it may not have been as much as you think.

 

[benm2010]

CYA doesn't degrade nearly that fast, more like 5ppm per year.

Do you know how much CYA the PB dumped in the pool to start with? If you don't, it may not have been as much as you think.

Chem Geek posted a few time (the simplest being here and more in depth here about CYA degrading anywhere from 2-10 ppm per month. Is that not accurate?

 

[PoolFool.]

CYA degrades, Who'd a thunk?
You guys are great, that explains a lot. The second post quoted above,

Degradation of Cyanuric Acid (CYA))

Goes into details at the bottom of the first page. Basically for summer degradation the primary drivers are temperature of the water and chlorine being near the shock levels. My chlorine is frequently that high as I raise it to that level often before heading out of town on a trip.

 

[tstex]

My CYA decreases mainly after huge rains and my pool drain is taking out the water to the street - this dilutes the CYA ppm bc pure rain water is mixing w pool water and leaving...I have never heard of CYA degrading at a rate of 10PPM per month under any circumstances given normal operating conditions. Can someone confirm ? thank you

 

[mknauss]

I have never heard of CYA degrading at a rate of 10PPM per month under any circumstances given normal operating conditions. Can someone confirm ? thank you

Oh yes. With elevated pool water temperatures you can get CYA degradation. It is greater if your FC is held above target level at the same time.

Spas lose CYA as they contain warm water. Our pool here in the desert loses up to 15 ppm per month in the summer.

 

[tstex]

Oh yes. With elevated pool water temperatures you can get CYA degradation. It is greater if your FC is held above target level at the same time.

Spas lose CYA as they contain warm water. Our pool here in the desert loses up to 15 ppm per month in the summer.

Thanks Marty - Just learned something - w 104 to 105 degree heat, my pools temp has skyrocketed...CYA on order

 

[Rocket J Squirrel]

My pool temp has been in the low 90s. So it seems pucks aren't so evil, after all, and can be used sustainably when appropriate.

 

[mknauss]

My pool temp has been in the low 90s. So it seems pucks aren't so evil, after all, and can be used sustainably when appropriate.

Sure. But you have to supplement with liquid chlorine. And test. Pucks cannot maintain your FC high enough without adding more CYA than what you lose from degradation.

And this only works in warm water areas. Ours also is in the low 90's.

 

[getreal720]

The pucks were never evil


They get a bad rap because people, often industry "experts" and pool maintenance contractors, don't really understand pool water chemistry or at least they don't understand the fact that these "pucks" contain CYA and will somewhat swiftly increase your CYA levels beyond those that are feasible or even possible to work with.


If you have enough sunlight exposure, and your weather is hot enough on average.... then yes your CYA "loss" may be enough to offset a large portion of what the pucks are adding. If you can do that, then your A OK to use the pucks. Even then, it probably won't be enough to be a sole use product.

The problem is a lot of folks aren't in a situation where enough CYA dissipates... and their levels drift up towards being unmanageable... and the pool turns a nice lovely green. Not really the products fault... just a lack of knowledge by those using it at times.

 

[Rollercoastr]

I love using pucks! I didn't feel comfortable using them until I fully-committed to liquid chlorine though, so using the pucks has introduced another learning curve. Just when I got really good at predicting what all of my test results would be, I started using pucks and my ability to predict all but disappeared. I use them during the off-season and while away. I've used the last of my powdered CYA and my goal is to not purchase more. I plan to manage ideal CYA levels using pucks.

I'm getting better, but they still mess with me. I wonder if the Clorox pucks I'm using are too big for my smaller pool. When fresh, a puck will spike FC and maintain pH. As the puck diminishes, FC levels off, but pH starts to climb. This week I saw pH > 8.2 for the first time in over two years!

I considered looking for smaller pucks, but that would reboot my methodology all over again...

 

[mknauss]

Be careful using Clorox pucks. Many have copper in them. Never use a product that has the word 'Blue' in the name.

 

[tstex]

Be careful using Clorox pucks. Many have copper in them. Never use a product that has the word 'Blue' in the name.

+1..Copper-sulfate is the primary ingredient in what many lake mgmt. companies apply into stationary bodies of water to prevent/limit/slow down vegetation growth. That's why you see "blue community of lakes" and similar. Copper has it's place, but not in pools 99% of the time.

 

[Rollercoastr]

Mine are "Clorox Pool & Spa Active99"

99% Trichlor 3" tablets

They also offer "blue" which contain 5.95% "other ingredients"

I just searched for smaller ones. Seems that 3" dominates.