"Computerized" water testing.

Jump to latest Follow Reply
V

vetman85

0
Feb 14, 2016
42
McKinney. TX
This may be a bit much, but I need info about the relationship between pool company computerized water testing and chemical sales. I suspect one supports the other.

Anyway, had my pool installed in early 2013. Started with the Rainbow 320 tab feeder for chlorine. The pool company provides free Biogard computerized (ALEX) water testing whenever I want it. They also gave me a Poolmaster water test kit (no CYA tests in it). I tested my water a couple times per week and took a sample in about once a month. The manual and computer testing were close in readings most of the time. However, ALEX informed me that the impact rising CYA had wass, of course, on chlorine...but there was more emphasis on the impact on total alkalinity. Seems while my manual reading of TA was similar to ALEX, depending on the CYA number, the EFFECTIVE TA was 1/3 to 1/2 the manual testing reading. So, they always wanted to sell me between 4-18 (!) pounds of Balance Pak 100 (baking soda). Then, since the TA was higher after adding the Balance Pak, of course I had to add muriatic acid to reduce the pH.

The upshot of all this was I got lots of white scale developing on my colored paster pool steps and sides. I went back and forth with the builder and their plaster "experts" and they all agreed that it was the big, bad CYA's fault. The highest CYA number was 140. Allegedly (even with all the testing and chemical adjusting) the CYA was creating a condition where the water was "hungry" and pulling the calcium out of the plaster......hmmmmmmmmmmmmmm.

So, after listening to this for a while, I decided to drain a bit over half the pool, acid washed the steps and sides, and refilled. CYA now at 60. Also, ripped out the tab feeder and used the BBB method over the winter, relying just on test kit testing. No problems. This weekend I installed an SWG and (shudder) took a pre-salt water sample in for ALEX testing. Guess what....TA was way low and they want me to mix in 17.5 lbs of Balance Pak 100 and then reduce the pH by dumping in their "pH reducer" (they would like me to use their dry product in my salt pool rather than muriatic acid). I informed them my TA test indicated 120 ppm and pH was 7.4....so I was not going to do anything other than dump in the salt.

Anyway, after all this, I have seen the chart for calculating the impact of CYA on chlorine. Any guidance on the impact (or not) of CYA on TA? Also, anyone else have any experience with computerized water testing? Seems it's a great way to sell pool chemicals......:mad:
 
vetman85 said:
This may be a bit much, but I need info about the relationship between pool company computerized water testing and chemical sales. I suspect one supports the other.
Click to expand...
Sales are literally the only reason pool stores offer free water testing. It gets you in the door and then provides you with a printout of chemicals they want to sell you. It is a sales business, everything done in that store is to sell product. That machine has one job, to get you to buy Biogard products.

As for computer testing, it requires regular calibration that is rarely done or done well so it is as dubious as any other testing done in a pool store. It's recommended levels and chemical additions are entirely controlled by the store and/or the manufacturer.
 
I've been between test kits and decided to rely on store tests for the intrum. Even with regular calibration on expensive computer test equipment they can make mistakes and offer silly excuses. From the same equipment I had a CH of 234mg/L then after adding almost 4kg of CaCl the same equipment after calibration gave me a reading of 272mg/L. Apparently I have an olimpic swimming pool in my back yard! There pH as out and salt out by about 1200mg/L.

When in the store I would be told my my TA was too low but I'd just say "perfect that's where I want it to be." I use Pool School - Water Balance for SWGs for my goals for a SWCG pool and poolmath to figure out how much to use.
 
welp,
this type of story is exactly why we don't trust pool store testing, or PB's opinions on chemical issues.
I will admit that on rare occasion, a LPS or PB who knows what they're talking about will pop up. But that's not generally the case.

CYA has zero effect on TA and is not the reason you got scaling. Scaling is caused primarily by a combination of high pH and high CH.

TA is the measure of bicarbonate in the water. TA buffers how quickly (or not) the pH rises, but has no direct effect on calcium scaling or any other water parameters.

Having said that, you did the right thing by draining half the pool to lower the CYA. (you prolly had high CH which also requires water drain to lower it). Otherwise, you would soon be suffering from algae problems and the pool store would have said you have chlorine lock and advised you to drain the pool and start over and they would have told you that draining the pool every 2 or 3 years is normal. Which is hogwash.

Good luck with your SWG (you're gonna love that thing), and keep us posted on how lovely and troublefree your pool has become by testing your own water and using TFP recommended guidelines.
 
Thanks all..confirms my suspicions. My preferred methodology going forward will be incorporating TFP info and my personal test kit.

For info, both the manufacturer of the colored plaster finish and the Biogard "plaster experts" told me that CYA in excess of 100 ppm causes a false alkalinity reading (actual alkalinity being 1/3 to 1/2 of the measured reading). Low alkalinity creates a carbonate deficiency in the water which then draws calcium carbonate from the finish. Ultimately the pigment is also dissolved, resulting in a white blotchy surface. They both recommended water change and one recommended a light acid wash.

Anyway, I once took a sample of tap water in to be tested. The total hardness was 156. I have been told that the water here in north Texas is prone to being fairly hard, so I am contacting the local water district to see how the water quality varies over time. ALEX tests over the last year have given readings from 191 to 534, but, of course, I have no idea how well good old ALEX was calibrated.

While I did add a scale inhibitor monthly during last year's swimming season, I have only ever seen a slight scale buildup on the pool tiles at the waterline and on the edges of the waterfall....nothing really significant. My current working hypothesis, however, is that I should have gone with the usual el cheapo white plaster finish. We previously had a pool with white plaster in the Houston area. We used chlroine tabs, dichlor shock and had a DE pool filter. Never knew about or measured CYA. If any of the chemistry that the "experts" said was going on, white deposits on white plaster don't show up. Also, regular flushing of the DE filter created partial water changes that I don't get with my cartfridge filter. Life was easy then......

Now I am going to launch myself into uncovering the true realtionship between CYA and TA.......great life I lead...no....:confused:
 
I'll just cut to the chase and say you *really* need your own *reliable* test kit. I prefer the TF-100 along with the Speed Stir device which no one regrets once they use it.

The TF-100 or the Taylor's K-2006. Both available from PoolSupplyWorld.com or TFTestkits.net

And you need to delve into Pool School (link up at the top) and learn what chemicals do and which ones you need (and don't neeed!) along with ideal levels for your pool.

Your pool will sparkle like its never done before!
 
vetman85 said:
Now I am going to launch myself into uncovering the true realtionship between CYA and TA.......great life I lead...no....:confused:
Click to expand...

Let me see if I can help you here.

Total Alkalinity (TA) is defined as the sum of all chemical species in solution that can accept a proton (H+). The most obvious chemical reaction would be for hydroxides (OH-), e.g.,

OH- + H+ --> H2O

Other alkaline species in pool water are the carbonate anions (HCO3- and CO32-), the borate anion (B(OH)4-), the cyanurate anions (three different cyanurates and three different chlorinated cyanurates). Sulfates and fluorides are not typically found in pool water to any great extent. So, the TA would be defined as -

TA = [OH-] + [HCO3-] + [CO32-] + [B(OH)4-] + [cyanurates]+....

One can simplify the above equation by noting that, at pool water pH, there are only a few dominant alkaline species. For example, the [OH-] is small as is the carbonate ([CO32-]) species. As well, there is only one non-chlorinated cyanurate and one chlorinated cyanurate species that have any significant concentration in pool water; there will be denoted as H2CY- and HClCY-. So we can rewrite the above equation as -

TA = [HCO3-] + [B(OH)4-] + [H2CY-] + [HClCY-]

that is,

Total alkalinity = bicarbonate concentration + borate concentration + cyanurate concentration + chlorinated cyanurate concentration

When one performs the total alkalinity test using the Taylor reagents, you are basically using a know concentration of sulfuric acid (a strong acid) to titrate away all of the alkalinity. The indicator dye is designed to make the color transition from green at normal pH to red when the pH has finally dropped below 4.5. You then count the number of drops to make it to the transition and multiply that by a factor to give you the total alkalinity. The total alkalinity is reported in units of calcium carbonate concentration, or ppm of [CaCO3].

So why a pH of 4.5 and not some other pH?

The answer is that, at a pH of 4.5, more than 99.95% of the bicarbonate alkalinity has been converted to aqueous CO2 (which is not alkaline) and all of the other species will be exhausted as well.

So why is it reported as "ppm of [CaCO3]" ?

Because you need to choose a standard by which you calibrate the concentration of the sulfuric acid titrant against. In the Taylor test, each drop of R-0009 titrant can neutralize 10ppm of [CaCO3] for the specific volume of water used in the test.

So what is this "cyanuric acid correction factor" all about?

When when wants to calculate a calcium scaling index such as the calcite saturation index (CSI) or Langlier Saturation Index (LSI), one must know the carbonate alkalinity of the water involved. So, if you know the TA of the water sample, then you can subtract out a small factor for the cyanuric acid component of it to get a reasonable value for the carbonate alkalinity. However, TFP's PoolMath doesn't need to use any corrected TA values. You simply measure the TA as-is from the Taylor test kit and you put that number into Pool Math. Pool Math takes care of the rest of the correction factors internally.

At the end of the day, most of what you have written regarding the electronic tester used by that pool testing company proves what we at TFP already know - most PBs are good at building pools but know little to nothing about water chemistry. As well, all of the "chemistry advice" you've been given by them is utter nonsense. Their explanations of alkalinity and scaling are complete BS made up only to try to sell you very expensive baking soda (you can buy baking soda in the supermarket for less than $1 per pound. They sell you alkalinity increaser, which is baking soda, for four times that price). You would do well to never enter that store again and simply purchase your own test kit (Taylor K-2006 or TfTestKits TF-100) and ask this forum for chemical advice.
 
JoyfulNoise said:
Let me see if I can help you here.

Total Alkalinity (TA) is defined as the sum of all chemical species in solution that can accept a proton (H+). The most obvious chemical reaction would be for hydroxides (OH-), e.g.,

OH- + H+ --> H2O

Other alkaline species in pool water are the carbonate anions (HCO3- and CO32-), the borate anion (B(OH)4-), the cyanurate anions (three different cyanurates and three different chlorinated cyanurates). Sulfates and fluorides are not typically found in pool water to any great extent. So, the TA would be defined as -

TA = [OH-] + [HCO3-] + [CO32-] + [B(OH)4-] + [cyanurates]+....

One can simplify the above equation by noting that, at pool water pH, there are only a few dominant alkaline species. For example, the [OH-] is small as is the carbonate ([CO32-]) species. As well, there is only one non-chlorinated cyanurate and one chlorinated cyanurate species that have any significant concentration in pool water; there will be denoted as H2CY- and HClCY-. So we can rewrite the above equation as -

TA = [HCO3-] + [B(OH)4-] + [H2CY-] + [HClCY-]

that is,

Total alkalinity = bicarbonate concentration + borate concentration + cyanurate concentration + chlorinated cyanurate concentration

When one performs the total alkalinity test using the Taylor reagents, you are basically using a know concentration of sulfuric acid (a strong acid) to titrate away all of the alkalinity. The indicator dye is designed to make the color transition from green at normal pH to red when the pH has finally dropped below 4.5. You then count the number of drops to make it to the transition and multiply that by a factor to give you the total alkalinity. The total alkalinity is reported in units of calcium carbonate concentration, or ppm of [CaCO3].

So why a pH of 4.5 and not some other pH?

The answer is that, at a pH of 4.5, more than 99.95% of the bicarbonate alkalinity has been converted to aqueous CO2 (which is not alkaline) and all of the other species will be exhausted as well.

So why is it reported as "ppm of [CaCO3]" ?

Because you need to choose a standard by which you calibrate the concentration of the sulfuric acid titrant against. In the Taylor test, each drop of R-0009 titrant can neutralize 10ppm of [CaCO3] for the specific volume of water used in the test.

So what is this "cyanuric acid correction factor" all about?

When when wants to calculate a calcium scaling index such as the calcite saturation index (CSI) or Langlier Saturation Index (LSI), one must know the carbonate alkalinity of the water involved. So, if you know the TA of the water sample, then you can subtract out a small factor for the cyanuric acid component of it to get a reasonable value for the carbonate alkalinity. However, TFP's PoolMath doesn't need to use any corrected TA values. You simply measure the TA as-is from the Taylor test kit and you put that number into Pool Math. Pool Math takes care of the rest of the correction factors internally.

At the end of the day, most of what you have written regarding the electronic tester used by that pool testing company proves what we at TFP already know - most PBs are good at building pools but know little to nothing about water chemistry. As well, all of the "chemistry advice" you've been given by them is utter nonsense. Their explanations of alkalinity and scaling are complete BS made up only to try to sell you very expensive baking soda (you can buy baking soda in the supermarket for less than $1 per pound. They sell you alkalinity increaser, which is baking soda, for four times that price). You would do well to never enter that store again and simply purchase your own test kit (Taylor K-2006 or TfTestKits TF-100) and ask this forum for chemical advice.
Click to expand...

I am converted. I did get an abbreviated version of your CYA explanation on the Taylor Technologies website. Then upon Googling the relationship between CYA and TA, I was directed to a TFP page wherein I discovered the evolution of Pool Math and the fact that the various corrections are internally calculated. So, as I have a TF-100, I shall faithfully use Pool Math and spend the rest of my time lounging in the pool............:calm:
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply