Api Test Kits

[Susan Edwards]

Okay, never found the answer to this. When I use a syringe, a real one, and measure out 5 ml water and add it to the test tube, it is over the line. Which means the api test tubes are just shy of 5 ml

So, do you go by the line on the tube, or the measure of the syringe. I get them on amazon and assume they are accurate. Anyone else notice this? And what do you go by?

Also, reading the color is so subjective. You can get different readings by:

Holding tube up to the colors but not touching card
Holding tube against the white background
Standing the tube next to the colors

If you hold the tube against the white background it is darker
If you hold it to the light iwth white behind, it is lighter
If you lay it down on the white background, darker

so how do you read the color?

 

[Flippers4pups]

I found that most syringes, the ring on the rubber plungers are the accurate line to measure by. Try pulling some fluid up to the ring at 5ml and put it in the test tube and see what it reads.

 

[timnem70]

Yep. They are like that. It's what's called a miniscus curve and is an optical illusion of sorts. Your syringe is the correct one amd yes, it does look like it is about 1ml above the 5ml line on the API vial.

 

[Susan Edwards]

Thanks @timnem70 You'd think api would make their tubes better. The hanna vials are right on the money with their lines

 

[RobZilla04]

The hobby grade test kits should not be considered exact in either their measurements or results. Rather they give a "good idea" or range for a particular value. Each has its margin of error whether expressly printed or not. Additionally the volume of water and minimal measurement targets are far from what could be considered scientific. Take the powder used in the Hanna kits. Leave a small amount of granules behind and place slightly over 9ml of RODI sample with 1ml reagent A and your Cal value is immediately off by ? who knows for sure.

Shoot for consistency within the desired acceptable ranges and try to minimize human error by testing the same each and every time. Doesn't hurt to use a second test kit to confirm or dispute a wildly sporadic single test.

As for the question at hand, each is typically off from another. One brand vial compared to another is slightly off from what I've found.