Salifert Test Kits - Quick Question

[socalmonty]

I have been using Salifert kits to test Alk, Ca, Mg, Phosphates and Nitrates for about four years. I just replaced my Alk, Ca and Mg kits and the reults for Ca and Mg are off the charts. My old kits had Ca at 450 and Mg at 1425. With the new kits Ca is 500+ and Mg is 1500+. Scary... The new kits have smaller measuring spoons. Can anyone confirm that you are still supposed to be using level spoonfuls of the powders or if they are now heaping spoonfuls? Just trying to get to the bottom of my issue. User error, testkit error or truly high readings. Thanks! Doug

 

[Habib]

I have been using Salifert kits to test Alk, Ca, Mg, Phosphates and Nitrates for about four years. I just replaced my Alk, Ca and Mg kits and the reults for Ca and Mg are off the charts. My old kits had Ca at 450 and Mg at 1425. With the new kits Ca is 500+ and Mg is 1500+. Scary... The new kits have smaller measuring spoons. Can anyone confirm that you are still supposed to be using level spoonfuls of the powders or if they are now heaping spoonfuls? Just trying to get to the bottom of my issue. User error, testkit error or truly high readings. Thanks! Doug

The newer spoons (since about a year) are smaller but the powder is more concentrated.

Actually, with the calcium and magnesium kits it doesn't matter if it is a level spoon or say 50% more or less. The endpoint/colorchange will be at the same point. The only difference will be the strength of the color.


Having said that, some see a effect of higher readings when starting with a new kit. That is usually caused by letting the reagent of the previous kit evaporate somewhat. For example by accidentally not closing the cap properly. This concentrates the reagent resulting in a lower reading.


If you want I can send you a certified reference solution for magnesium and calcium.

 

[socalmonty]

Thanks for the help, Habib. That was a really quick response! It would give me a lot of peace of mind if I could test my results against reference solutions. Please let me know how I can get them.

 

[Habib]

Thanks for the help, Habib. That was a really quick response! It would give me a lot of peace of mind if I could test my results against reference solutions. Please let me know how I can get them.

Please pm me your name and address.

 

[socalmonty]

PM sent. Thanks again!

 

[socalmonty]

Just an update on my issue. Habib from Salifert graciously sent me a bottle of reference solution for Ca and Mg and I was able to confirm that both my old test kits had gone bad. In the process of sorting it all out, Habib gave me some very useful suggestions regarding the Mg testing process to improve the acuracy of the results. I found that I was making mistakes in the way I was testing that resulted in a 50ppm overstatement of my Mg readings. I thought it might be helpful to others to see his suggestions as well. I'm sure I'm not the only one who purges the 2mL syringe to get rid of the air before I fill it with sample water.

Here are the suggestions. They can also be generally applied to the other Salifert kits.


Test kit tolerance with titration kits is typically +/- 2% or less. With a minimum of one drop resolution.

Some users make the mistake of purging the 2 ml syringe in order to remove air. If you do that then the results will be too high by approx 2%. For magnesium that would translate to approx 30 ppm too high.

Unlike calcium, the magnesium color change is slow. Near the end point make sure to swirl better of a few seconds longer. Not doing so will result in overtitration giving approx one drop resolution too high value. One drop in the magnesium is approx 15-20 ppm.

When dropping the Mg-1 reagent from the dropperbottle, make sure that the 5 drops are added by holding the dropperbottle as vertical as possible.

 

[Habib]

Read your pm just now. You're finding 1300 ppm on the certified 1285 ppm magnesium standard. A 1% deviation is very good. :thumbsup:


To add a few more suggestions for test kit users:

The only reasons the titration liquids (like ours) can go "bad" is by contamination by e.g. accidentally putting back remaining reagent in the wrong bottle. Using one kit at a time helps avoiding this.
And by allowing the reagent to evaporate. Accidentally forgetting to tighten the cap after use will cause evaporation, this effect will be worse if not much reagent is left.

The problem with doing things accidentally is that they go often unnoticed.

Evaporation causes the titration reagent to get more concentrated, requiring less to reach the color change endpoint, resulting in a lower than actual value.

 

[socalmonty]

Thanks, Habib.

 

[Habib]

Thanks, Habib.

You're welcome Doug!

And thank you for your efforts and kind words.

 

[MarineSniper]

All I use are the Salifert kits and they seem to be the most accurate and consistent. I recently purchased a hobbyist's entire setup and it had some older kits. I suspected they were expired but was curious as to how well they would read. VERY big difference! As with any product, you definitely want to replace them at the recommended time!