I have been using Salifert for my KH/Alk and Ca tests, the problem I noticed with these tests is at step 3. (the part in red)
Put the plastic tip firmly on the 1 ml syringe. And draw into the syringe the KH reagent (ensure that the end of the plastic tip is constantly submersed in the KH reagent) till the lower end of the black part of the piston is exactly at the 1.00 ml mark. There will be some air present just below the piston. This is the air which was present between the end of the plastic tip and the piston. This will not influence the test result.
It seems like an inaccuracy would have to happen because the amount of air present in the syringe is different every time I do a test, sometimes the air gap is as little as 0.01ml and sometimes it's more than 0.15ml. That comes out to a difference of about 2.2 KH.
The KH/Alk test does come with a check solution, so I used that to calibrate the test using the liquid line rather than the syringe's "black piston", that way it takes out the air gap problem. But the Ca test doesn't have the check solution and it seems the less testing solution you have left the more inaccurate the tests get.
So does anyone else using Salifert tests have this problem or am I missing something? And can anybody suggest better tests? Thanks for any help.
Hey Pat. I have used the Salifert quite a bit. I believe they are pretty accurate and recommend them. As far as the plastic tip for the syringe, even with the tip on, you are drawing back a volume of 1 cc/ml which is the amount that would be in the plastic tip. I believe that they used this tip to increase accuracy due to the small droplet produced by it.
But, I too wanted to insure the accuracy of testing my parameters. I started switching over to HANNA meters. They have several different meters (Phos, Alk, Calcium, etc.) and give you an actual measured number. Just feel better having an actual value. Hope this helps and good luck.
Well you should only get into an inaccuracy if you were to get down the point where the air gap is being dispensed. Second you can get more consistent by drawing a full syringe and then push it right back into the bottle hard, some of the air will then leave the syringe. But really it's a non issue unless your pushing air out of the syringe while still doing the titration. You will still have moved as much titration fluid into your sample as compared to the syringe being completely full of fluid. Does that crap make sense, lol. Bottom line if you don't see air bubbles in the syringe tip then your just fine.
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