Calcium Hardness Results

[C4ST]

Any thoughts on why I am consistently getting results for calcium hardness that are higher than two local Leslie pool stores? I am consistently getting results in the range of 275 to 300 ppm, and two separate Leslie pool stores are consistently getting results of 200 ppm or less (170 ppm today). I have a TFTest kit, and I noticed Leslie uses a different method--they add an eye dropper full of a reagent, add 5 (?) drops of another reagent that turns the solution red, and then add a final reagent until the solution turns blue. They then multiply the number of of drops by 10 to get the ppm of hardness.

Note that my Cyanuric acid level has been dropping recently, which would seem to indicate dilution of my pool water--we have had a number of days of heavy rain such that I've had to drain water from my pool. Yet during this same time period, my hardness results have not been dropping, which makes me concerned that my test results are not accurate.

I have fresh reagents that I bought this year, and I'm following the test instructions as carefully as possible.

Any thoughts?

 

[JoyfulNoise]

Because you're doing the test correctly and they are not....

From your description it doesn't sound like they are being very precise. If one follows standard calcium hardness testing protocols, the initial addition of "buffer" (it's just sodium hydroxide to raise pH) has to be done with a certain amount of accuracy. When you add the R-0010 you are raising the pH to approximately 10.5. That gets rid any magnesium interference but doesn't affect the calcium levels. If one were to be careless with that setup and inadvertently raise the pH up above 11, then calcium carbonate will start to precipitate out of solution and you'll cause a false low CH value.

This is exactly why TFP tells users NOT to cross-check themselves with pool store results. YOU are doing your testing just fine and YOU need to believe in yourself that you are doing it right. Doubting yourself and going to the pool store to "double check" is only logical if pool stores can do the testing just as good or better than you can. The trouble is, they don't ever do testing as good as the pool owner does and there is no incentive for them to do a good job because if they get values that are wrong, then they have a very nice computer print out that will tell you all of the chemicals you need to buy RIGHT AWAY so that your pool doesn't melt into the earth....

Ditch the pool store testing and only go in there when you need to buy something that you can't find elsewhere....

 

[crabboy]

Did they follow their test with the words: "The calcium hardness increaser is on that back wall, grab two and a bag of all purpose super shock" ?

 

[C4ST]

Thank you for your feedback and I certainly share your feelings about pool store testing, and I rarely get my water tested at a pool store. The only thing in this case that concerns me is that my cyanuric acid concentration has dropped recently, corresponding with heavy rain. As I understand, the only thing that causes cyanuric acid concentration to drop is dilution. But dilution (with rain water) should also cause calcium hardness to drop, should it not? And my calcium hardness as measured by me has not shown a drop, while the pool store readings have shown a decrease. This is what prompted my question.