Squeeze last bit of life out of cell?

Jump to latest Follow Reply
I never trust any single test.

I always want to see several tests that are in close agreement before I will trust a reading.

I will usually use the SWG, a meter and a K-1766 to test to make sure that they are all in agreement.
 
  • Like
Reactions: Saturn94
JamesW said:
Seems like the K-1766 is off for some reason.

Maybe try a different bottle of reagent.

Maybe the drop size is off for some reason?

Maybe an interference, but I don't know what would interfere.
Click to expand...

Thanks for the response.

I did replaced my K1766 reagents but got the same result. The old reagents had not expired and the new reagents are even fresher (exp date far out). Btw, I keep everything inside the house in a cool dark place.
 
I don't know if this is relevant, but worth a look.

Orthophosphate at concentrations greater than 25 ppm will precipitate as silver phosphate to cause positive interference. This can be prevented by diluting orthophosphate concentrations below 25 ppm with DI water. Bromide, iodide, and cyanide at all levels titrate as equivalent chloride concentrations. Sulfide, thiosulfate, and sulfite interfere but can be removed by treatment with hydrogen peroxide. Quats may interfere; to prevent add 10 drops of R-0884.
Click to expand...

https://www.taylortechnologies.com/...de-argentometric-1-drop-200-ppm-75-oz--K-1766
 
  • Like
Reactions: Saturn94
Did you use a SpeedStir?

If you are doing the test y hand, it can be very difficult to get repeatable droplets and can lead to droplet size variations.
 
Here's another thing you can try - use a 20mL water sample and each drop of regent will represent 100ppm. If you want to be really precise, you can use a 40mL water sample and each droplet of reagent will be 50ppm/drop.

Also, make sure you are stopping the test as soon as the color goes from cloudy straw yellow to any kind of brownish-red. If you keep adding drops of reagent, you can get the color to change more towards a salmon red but that's not the correct end-point. The correct end-point for the test is when it transitions from cloudy yellow to brownish-red.
 
  • Like
Reactions: mas985
JoyfulNoise said:
Did you use a SpeedStir?

If you are doing the test y hand, it can be very difficult to get repeatable droplets and can lead to droplet size variations.
Click to expand...

No. I do make sure to mix thoroughly between drops as I know rushing the drops and not mixing thoroughly between drops can result in a false high reading. I also noticed in this Taylor video they do not use a SpeedStir.


I’m confident I’m swirling/mixing very well, certainly better than the guy in the video demonstration.

Question….how does using the SpeedStir effect drop size? 🤔
 
Last edited:
JoyfulNoise said:
Here's another thing you can try - use a 20mL water sample and each drop of regent will represent 100ppm. If you want to be really precise, you can use a 40mL water sample and each droplet of reagent will be 50ppm/drop.

Also, make sure you are stopping the test as soon as the color goes from cloudy straw yellow to any kind of brownish-red. If you keep adding drops of reagent, you can get the color to change more towards a salmon red but that's not the correct end-point. The correct end-point for the test is when it transitions from cloudy yellow to brownish-red.
Click to expand...

Thanks for the suggestions.

I do stop the test as soon as it transitions from cloudy yellow to brownish red as you said and as indicated in the Taylor video. The transition is pretty dramatic, so it’s easy to see.👍
 
Using a SpeedStir simply relieves you of the necessity of having to swirl a liquid while trying to add drops from a reagent bottle. While you may think you're pretty good at patting your head and rubbing your belly at the same time, most people can't sustain that for any length of time without starting to wander off. I consider myself to be very good at hand-swirling because I've been doing it since my college days and I have worked in and around chemistry labs all my life. Even with all my experience, I still use a SpeedStir because I can then focus on adding the drops slowly and repeatedly without variation in volume. If you're constantly swirling, putting the test tube down, squeezing out a droplet, swirling to mix, etc, etc, your reagent droplet sizes are much more likely to vary drop to drop giving you more or less reagent with each drop. People also tend to squeeze these dropper bottles too hard which results in a droplet size greater than 40uL (that's the nominal volume for each droplet). The dropper bottle should be squeezed only hard enough to get a droplet to start to form on the tip and then let gravity take over. It's a matter of precision and practice and it's not at all as easy as the videos depict because the guy in the video from Taylor, Wayne, has tons of lab experience. This is why TFP ALWAYS recommends getting a SpeedStir ... it makes all of the tests dramatically easier to perform.
 
  • Like
Reactions: Saturn94

Enjoying this content?

Support TFP with a donation.

Give Support
JamesW said:
I don't know if this is relevant, but worth a look.



https://www.taylortechnologies.com/...de-argentometric-1-drop-200-ppm-75-oz--K-1766
Click to expand...

I saw that and wondered about it since I use Jack’s Magic Purple stuff on a regular basis. I tested phosphates with a Taylor drop test and came up with 2000ppb. Isn’t that the equivalent of 2ppm, or am I getting my decimal places mixed up? 😯

I didn’t quite understand from the article if high phosphates would cause a false high or low reading.
 
Phosphates will react with the silver ions and chelate them, taking them out of the reaction with the potassium chromate. This will cause a false - high reading because it will take more drops of silver nitrate reagent to overcome the chelating agent.

If you are using sequestering agents, then that's a problem because they will also cause a false high reading. That is where your error is coming from. You have both phosphonate and phosphate in the water. Both of those will chelate silver.

Typical maintenance doses of phosphonate sequestering agents add as much as 25ppm HEDP to pool water to control metal scaling.
 
  • Like
Reactions: Saturn94
JamesW said:
Add pool water to the 10 ml mark and then add distilled water to the 20 ml mark and do the test again.

The multiplier will still be 200 ppm per drop.
Click to expand...

I’ll give that a try. Since the pool sample would be diluted by half, how is it the multiplier would be the same? 🤔
 
JoyfulNoise said:
Phosphates will react with the silver ions and chelate them, taking them out of the reaction with the potassium chromate. This will cause a false - high reading because it will take more drops of silver nitrate reagent to overcome the chelating agent.

If you are using sequestering agents, then that's a problem because they will also cause a false high reading. That is where your error is coming from. You have both phosphonate and phosphate in the water. Both of those will chelate silver.

Typical maintenance doses of phosphonate sequestering agents add as much as 25ppm HEDP to pool water to control metal scaling.
Click to expand...

Thank you for that explanation. 😀👍 Previously, I posted a list of what I add to the pool and asked about possible interferences, but I guess it got lost in the crowd. 😉

While it explains why the K1766 is reading higher than everything else, it doesn’t account for the high result testing the 3000ppm calibration fluid. I guess that might be attributed to a combination of testing method (manual swirling) and the K1766 stated +/- 200ppm error range?

EDIT: I just remembered something I left off my chem list. At closing I add a quart of polyquat 60%. Would this also be an issue?
 
Last edited:
JoyfulNoise said:
Phosphates will react with the silver ions and chelate them, taking them out of the reaction with the potassium chromate. This will cause a false - high reading because it will take more drops of silver nitrate reagent to overcome the chelating agent.

If you are using sequestering agents, then that's a problem because they will also cause a false high reading. That is where your error is coming from. You have both phosphonate and phosphate in the water. Both of those will chelate silver.

Typical maintenance doses of phosphonate sequestering agents add as much as 25ppm HEDP to pool water to control metal scaling.
Click to expand...

I take it the AquaChek salt strips aren’t affected by this since they use a different method?
 
Saturn94 said:
I take it the AquaChek salt strips aren’t affected by this since they use a different method?
Click to expand...
Salt strips measure salinity through capillary action as the surface tension of salt water changes with salinity. Their biggest problem is that they are not terribly precise (error can be as high as +/-400ppm) and they are subject to spoiling if exposed to humid air.
 
  • Like
Reactions: Saturn94
Also, I generally don’t agree with the guidance that a discrepancy in the salinity measurement should be used as the deciding factor for whether or not a cell should be replaced. I haven’t looked at any of the Pool School articles that talk about that but I think that’s wrong. No SWG is going to measure salinity precisely. It may be an indication that the cell is nearing its end of life but whether or not to replace should be based on the cell working or not. If it’s generating chlorine, then who cares what the salinity readout says.

@Leebo do we have guidance somewhere stating that a cell needs to be replaced based on how erroneous the salinity measure is?? If so, that needs to change.
 
  • Like
Reactions: mas985
The salinity readout from the Aquarite depends on the performance.

The performance is determined by the readout as instant salinity divided by the actual salinity.

Once the performance drops below 75% it is generally time to consider replacing the cell.

You can make the cell work longer by changing the cell type to a smaller cell, but, in general, the cell has begun it's final stage of life.
 

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