Using titration test kit liquids to the last drop

[Jason K]

Ive been using salifert mag and Red Sea cal test kits for a few years now, and I don’t remember running into this problem before. I’ve been trying to squeeze out the last few test on each (on my weekly testing schedule) and have seen consumption steadily increasing on both for the last several months, and so have been increasing supplementation accordingly. Thought it was odd but I rationalized it somehow. Just opened up a fresh box of both tests, and my readings were so off it’s alarming.

Cal- old kit 340/fresh kit 475
Mag- old kit 1290/fresh kit 1485


Lesson learned I guess. Is this a common problem others have run into? I’m trying to out how I’m diluting/contaminating the titration liquids.

 

[shakacuz]

as you get closer to the end of the reagent, results tend to fluctuate. i've had this occur with my hannah egg checkers. mainly with the PH, CAL, and ALK, so i'd wager this can occur with other vendors/types of test kits

 

[Randy Holmes-Farley Verified Community Expert]

Ive been using salifert mag and Red Sea cal test kits for a few years now, and I don’t remember running into this problem before. I’ve been trying to squeeze out the last few test on each (on my weekly testing schedule) and have seen consumption steadily increasing on both for the last several months, and so have been increasing supplementation accordingly. Thought it was odd but I rationalized it somehow. Just opened up a fresh box of both tests, and my readings were so off it’s alarming.

Cal- old kit 340/fresh kit 475
Mag- old kit 1290/fresh kit 1485


Lesson learned I guess. Is this a common problem others have run into? I’m trying to out how I’m diluting/contaminating the titration liquids.

I would not assume that the results changed just due to the last of the fluid. If that were the case, you would have seen calcium and magnesium appear to drop rapidly in the last few tests.

 

[Jason K]

I would not assume that the results changed just due to the last of the fluid. If that were the case, you would have seen calcium and magnesium appear to drop rapidly in the last few tests.

That’s what I meant. Steadily dropping test values is what I meant by assumed steadily increasing consumption.

 

[Jason K]

That’s what I meant. Steadily dropping test values is what I meant by assumed steadily increasing consumption.

And to be clear, I ran each of those tests today. The discrepancies in the values was based on the same sample water

 

[taricha]

I would not use the last few mL of a titration fluid in a container that's been opened and closed many times. I just wouldn't expect a small amount of liquid in a large repeatedly opened bottle to maintain its concentration.

 

[Jason K]

I would not use the last few mL of a titration fluid in a container that's been opened and closed many times. I just wouldn't expect a small amount of liquid in a large repeatedly opened bottle to maintain its concentration.

But why? Dry syringes go in, pull out the liquid, and nothing gets put back in. Evaporation has to be negligible.

I guess the “active” ingredients in the reagent break down or something.

 

[Jason K]

Another example, both test done at the same time

Hanna Alkalinity:
bottom of the bottle (test #25): 8.6
New bottle (test#1): 7.8

I mean, come on…

 

[Randy Holmes-Farley Verified Community Expert]

Hanna reagents have a surprisingly poor track record of stability. I keep nitrate and phosphate packets in a fridge.