TA Rock Solid, CYA seems to remain low

[Pwis]

Hi folks,

I’ve got a couple general questions about my test results using my TFP 100. I’ve noticed my alkalinity really hasn’t changed from about 100 for the last six months or so. This is using the trouble free 100 kit and I’m literally just counting the drops until the color doesn’t change any further. Then multiplied by 10.

I’ve had to add zero baking soda to this pool for about 6 months which I find odd and I’m starting to question whether it’s true or not. I went into Leslie’s (I know) to get an idea of what their instrument would read on my pool water and they told me my alkalinity was zero. I do run my chlorine a bit hot (15-20ppm) because I have a dog that likes to swim in the pool and if I don’t give myself a wide buffer I end up needing a slam the pool. As a result, my alkalinity test is often blue changing to yellow, but the kit says the test is still valid. I suspect their instrument can’t detect the alkalinity in the presence of higher chlorine levels.

At the same time, I can’t seem to keep my cyanuric acid up in the range where I want it
(70-80). I’m consistently reading between 50 and 60 even though I’ve added 3 pounds of cyanuric to this pool just a few weeks ago when my reading was between 50 and 60. The CYA test hasn’t really changed. I’ve probably added 6 or 7 pounds of cyanuric acid to my pool this year. Either with a sock hanging in front of a return jet, or I throw the sock in the skimmer basket.

I have not exchanged any water from my pool this year, so it’s not due to water replacement.

I suppose it’s possible alkalinity can remain steady for long periods of time and maybe I’m chasing the cyanuric acid because I keep a high chlorine level, but I would appreciate any thoughts on this.

Thanks

 

[PoolStored]

TA is typically influenced by the water that is added. Rain and fill water. Rain is likely 0 TA. Test your fill water for TA. My guess is that your fill water TA is close to the same as your pool.

What is your pool TA and what is your fill TA?

CYA will degrade about 5-10 per month. The loss can be higher if your pool water temperature is above 90.

What is the temperature of your pool water over the last month?

 

[proavia]

How old are your test kit reagents?
How/where do you store your test kit?

 

[reggiehammond]

I suspect their instrument can’t detect the alkalinity in the presence of higher chlorine levels.

If you read their notes, they report "alkalinity, calculated" which is influenced by CYA.

Not adding baking soda is not abnormal, once TA is 50-60, pH rise stops as equilibrium is found and you're pretty home-free.

Stay out of the pool store unless you enjoy confusion and poor testing accuracy.

 

[Pwis]

TA is typically influenced by the water that is added. Rain and fill water. Rain is likely 0 TA. Test your fill water for TA. My guess is that your fill water TA is close to the same as your pool.

What is your pool TA and what is your fill TA?

CYA will degrade about 5-10 per month. The loss can be higher if your pool water temperature is above 90.

What is the temperature of your pool water over the last month?

I can check the fill water when I get home but I’m not following your logic. I filled this pool in 2022. So I’m not sure why the TA in the fill water would matter at this juncture after a few years of balancing ph with muriatic acid etc. there’s been a couple of inches I’ve had to drain off from time to time after a heavy rain but I’d expect any influence of TA from the original fill water is long gone.

 

[Pwis]

How old are your test kit reagents?
How/where do you store your test kit?

Probably a year old. I store them in a covered patio inside that plastic tackle box they came in.

 

[PoolStored]

Do you have an autofill? You don't have any evaporative loss in Florida and have to add water?

 

[Pwis]

If you read their notes, they report "alkalinity, calculated" which is influenced by CYA.

Not adding baking soda is not abnormal, once TA is 50-60, pH rise stops as equilibrium is found and you're pretty home-free.

Stay out of the pool store unless you enjoy confusion and poor testing accuracy.

Yeah I knew their number was nonsense. I have noticed just anecdotally that their CYA reading is usually within 10% of what I am reading at home.

It is shocking how little they know about pool chemistry.

If you’re telling me it’s common to not need Baking soda more than maybe once per year then that sounds good. I expected with adding about 2 cups of acid each week that I’d need to add some baking soda more often.

 

[Pwis]

Do you have an autofill? You don't have any evaporative loss in Florida and have to add water?

No autofill. I have to add some water only occasionally, because we get a lot of rain. I’ll still check the TA on the fill when I get home as you’ve got me curious but I wouldn’t think adding a couple of inches occasionally would affect it too much.

I forgot to answer your other question. The pool water temp is around 85. But I added 3lbs of CYA 3 weeks ago and the measured value didn’t move from about 55.

 

[reggiehammond]

If you’re telling me it’s common to not need Baking soda more than maybe once per year then that sounds good. I expected with adding about 2 cups of acid each week that I’d need to add some baking soda more often.

I've never once added baking soda to my pool. But my fill water TA is higher than my pool water.

As you correct for pH (lowering from 8+ down into the 7's) you will lower TA. Once TA has reached equilibrium (normally around 50-60), your pH will stay in the 7's all the time. From there, you won't be adjusting pH, so you won't be affecting TA. Thus no need for increasing alkalinity via baking soda.

 

[proavia]

Probably a year old. I store them in a covered patio inside that plastic tackle box they came in.

Reagents should be stored in an indoor climate controlled environment - indoor air conditioned laundry room or similar.
Heat and cold will shorten their useful life.

 

[Pwis]

No autofill. I have to add some water only occasionally, because we get a lot of rain. I’ll still check the TA on the fill when I get home as you’ve got me curious but I wouldn’t think adding a couple of inches occasionally would affect it too much.

I forgot to answer your other question. The pool water temp is around 85. But I added 3lbs of CYA 3 weeks ago and the measured value didn’t move from about 55.

Source water TA is 40. So that doesn’t explain it.