Salifert Magnesium Test Kit???

[Fishturd]

I just bought the Salifert Magnesium Test Kit because I hear from everyone on here that Salifert is the way to go for Accuracy. I just did the test and if im doing my math right from their converstion table my Magnesium is way low. If anyone has this and know how it works it took me 45 drops from the syrinde to change the color from purple to blue and i figure my mag is a LOW 675?? Can anyone back me up on this, thanks?

[rachyl756]

As long as your calcium is within the paramiters of the test, I think it should be accurate. I ran the gambit of Salifert tests last night, wish I had done strontium before calcium since I basically tested calcium twice, but everything seemed to make sense with what I'm seeing in my tank. So I have no reason to believe that one is inaccurate.

[tdwyatt]

Originally Posted by Fishturd

I just bought the Salifert Magnesium Test Kit because I hear from everyone on here that Salifert is the way to go for Accuracy. I just did the test and if im doing my math right from their converstion table my Magnesium is way low. If anyone has this and know how it works it took me 45 drops from the syrinde to change the color from purple to blue and i figure my mag is a LOW 675?? Can anyone back me up on this, thanks?

At what mark on the syringe was the solution? tThe volume of a drop can vary dpending on whether you used the correct tip or not, and if you cleared the air from the tip as well so there is no compression effect to induce error into the test.

accurate testing using the kit depends on accurate measurement of the initial 3 ml sample, addition of the 6 drops of the MG-1 and good mixing, and accurate measurement of the Mg-2 (level spoonful using the spoon included with the kit). Although Salifert says it is ok to have air in the syringe (the way the instructions read, you may think this), but it is necessary to remove any air from the small syringe and totally fill it with the titration fluid to the 1ml mark without andy bubbles. Make sure to swirl between each addition of titration solution to the sample, and watch for the conversion to blue-grey.

This is the endpoint of the titration, record hou much solution is remaining in the syringe, and SUBTRACT this value in 100ths decimal form from 1.00:

You check the syringe and see that 0.25 is where the edge of the black plunger is in the barrel of the syringe. you subtract 0.25 from 1.00 too determine that you've used 0.75 ml of solution to titrate to the endpoint color change--

.

1.00 - 0.25 = 0.75 ml (amount used)

PPM Magnesium = amount used (see above) x 1500

0.75 ml x 1500 PPM/ml = 1125 PPM

.

When you say you used 45 drops, this doesn't really tell us much. The actual amount used in milliliters to the hundredths of a ml will be needed to accurately determine what the value for magnesium actually is. Remember, the amount left in the syring is just that, the mount LEFT OVER, NOT THE AMOUNT USED. We need to subtract this amount LEFT OVER from 1.00 to determine how much was actually used in the titration to calculate by the formula, but you can use the amount left in the syringe to determine the vaue if you use the chart included in the box with the instructions. The first column is the amount left in the syringe, the second column is the corresponding amount of magnesium indicated by the results.

Tell us what the amount left in the syringe actually was. Perform the test three times and compare your results. Post the actual salinity of the water column as well (as tested with a refractometer or temp corrected bulb hydrometer)

[Fishturd]

Tom, I did what you said and read the end of the black plunger and it changed color at 0.15 ml. subtract that from 1.00 gave me 0.85 x 1500=1275. Sounds alot better than my first answer. And my SG is right on the money at 1.024, temp 77.8, PH 8.3, cal is 400. Need to raise cal a bit.

[tdwyatt]

good deal, at least there isn't some gremlin running through the house with the magnesium magnet...



...oh WAIT!, that kinda looked a little like a certain TRT mod with the number 15000 tattooed to his forehead...

[Habib]

Tom,

Thanks for helping Fishturd out.


but it is necessary to remove any air from the small syringe and totally fill it with the titration fluid to the 1ml mark without andy bubbles.

It is not necessary to remove the air. Actually removing it might give inaccurate readings in the next measurements.

[Fishturd]

Thanks guys!!

[tdwyatt]

Originally Posted by Habib

<<(originaly posted by Tom)but it is necessary to remove any air from the small syringe and totally fill it with the titration fluid to the 1ml mark without andy bubbles. >>

It is not necessary to remove the air. Actually removing it might give inaccurate readings in the next measurements.

Habib, I started this post to say that including air in a measured volume would induce instant error, and proceeded to do the math to show this, but even with the air in the syringe, unless you change mid-measurement and try to calculate based on a volumetrioc delivery of a calculated volume, the bubble is consistant throughout the titration, and, as you said, the bubbles do not affect the results (ALTHOUGH if I could see how compression of the bubble might have some effect, I guess I'd be splitting hairs... )

This was the process...

Originally Posted by tom

If we pull up exactly 1.00ml of solution in our syringe, and there is a bubble included that accounts for 0.05 ml of the solution, we will actually have 0.95 ml to start our titration. Suppose that we titrate until our syringe shows that we have 0.25 ml left at endpoint. Calculating by the instructions with the kit, we would say that we used 0.75 ml, based on 1.00 ml(measured) - 0.25 ml(observed) = 0.75 ml(calculated). In actuality, we started with 0.95 ml, and we ended up with 0.20 ml, so our actual use was 0.95 ml (actual) - 0.20 ml (actual) = 0.75 ml (actual calculated)...


hmmm...

Nothing like establishing veracity by kicking your own butt, as they say...


Thanks for the comment, I had never really thought it through. For the benefit of others reading this, I must add that if you're using a syringe to deliver a specific volume, or a dose based on gm solute/ml solvent, that the dose must be free of air to deliver an accurate dose, but for this titration, the error is consistant throughout the procedure, so it is moot.