Discrepancies with TF-100 Test Kit

[Aqua_Man]

Ok, just received my TF-100 test kit and am having big discrepancies on a couple of tests.

Calcium hardness results from Leslie's reads - 260
Calcium hardness from test kit - I stopped adding drops of R-0012 after 67 drops (fluid still pink)

FC results from Leslie's - 3.0
FC results from test kit - 8.0

Anyone have a clue why such big discrepancies?

Everything else matched.

PH - 7.8
TA - 90
CYA - 35

I have a salt generator if that means anything.

 

[duraleigh]

Unless you have reason to believe your CH is 600+, I would suspect a testing error on the CH test. Review your procedures and, if you have done the test correctly, post back and we'll sort it out.

Assuming you used the FAS/DPD test from the kit, you can just about take it to the bank. It is about the most accurate FC test you can buy and is virtually never innaccurate.

Why Leslies doesn't match is probably because they do not use that same test.

 

[Guest]

could be static. A few things to try
Wipe the dropper tip with a damp tissue between drops.
make sure the bottle is upside down and not sideways when dropping drops.
let the drop form by itself instead of squeezing it out.

 

[JasonLion]

FC can be lost from the sample while you are on your way to the pool store. It is also completely possible for the pool store to make testing mistakes. Pool store testing mistakes are much more common than most people suspect.

 

[reebok]

I was told for months by the pool store that my CH was 399. I have no idea how they got such an exact number, but they have a big chemistry set and they're always nice, so I had no reason not to believe it. the other pool store gave me almost the same result. (though they were off each other by 2ppm on the free chlorine). when I tested CH myself, I gave up a few times, and then went the whole way and got a reading of 620ppm. there is a shorter way to test that waterbear told me which gave me almost the exact same result, which helped me verify and believe my high result. I recommend trying it that way and seeing what you get. then you can try it the normal way and see if they're close. my fill water is something like 40ppm CH, so I can only assume the pool builder (when I replastered in late 2007) put way too much calcium in the pool. this is a quote from waterbear:
1. with high CH you can do the test this way--10 ml water sample, 10 drops of first reagent, 3 drops of indicator, and then when you titrate each drop of titrant is 25 ppm CH instead of 10 ppm. You lose some precision but when you have very high calcium like yours it really does not matter that much if your CH is 620, 625, or 630 ppm (or even 600 or 650!)

also, according to pool school (pool-school/) you need more CYA.

 

[Aqua_Man]

Thanks for the replies. I'll re-test tomorrow using some of the suggestions. Thanks again.