Salifert Alkalinity Test Kit Question

EddieJ

EddieJ

Premium Member
Just tried a Salifert ALK test for the first time as I have been using LaMotte. The instructions say to place the plastic tip extender onto the 1ml syringe and then draw in the KH reagent. There is an air gap of about .2 (meaning the piston is at 1.0ML and the reagent is at .8), that does not seem correct to me. The instructions say that this will not effect the test but it appears to. When I perform the test it gives me a result of around 11 dkh if you go by where the piston is. But if you add the .2 it gives a result of 8.3 dkh and that is around where my LaMotte reads at. So my question is how large of an air bubble is acceptable? if you do not put the extender on and draw in the bubble is around .05 ml or so..
 
Highlander,

I am using Reef Crystals. The size of the air bubble has to affect the outcome of the test. If it was .4 instead of .2 that is a different amount of reagent being put into the test vial thus the endpoint would be affected.

So if they are compensating for that .2ml of air and the kit is reading correctly at 11dkh, then man is that a big difference compared to the LaMotte kit which gives a result of 8.3.
 
The Salifert kits operate based on the amount of solution added. You just need to use the same reference point at the beginning and end. So if you draw in solution such that the plunger starts at 1.0 ml, then titrate, and the plunger stops at .2 ml, you have added .8 ml regardless of the air bubble. The charts are designed assuming you start at 1.0 ml, therefore you just read the number of where it stops.

Todd
 
I'm still not getting it, maybe I am dense LOL!!

You start with a fixed volume, which is the syringe. You now fill it up with 1.0 ML of reagent with NO air at all. You have 1.0 ML of reagent. You depress the plunger and it travels to .1. You have added .9 ML of solution to the vial. Now you fill the the same syringe with to the 1.0 ML mark, but this time you have an air pocket occupying .3 ML of the syringe. You depress the plunger and it travels to .1 again. This time you have dispensed .6ml of reagent because .3 of the volume was filled with air.

But you are right in saying that the bubble doesn't mean anything UNLESS you go past the amount of the air bubble. That would affect the outcome no doubt, but at that point I guess you ALK would be REALLY high..

Now the really disturbing thing is that the 2 kits are so far off!!! Guess that's just what we have to deal with using this hobby grade kits. Stability is what we are looking for, so if it's in the acceptable range I guess we are good to go.
 
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When the black plunger starts at 0 and you suck in to 1ml then you will still only have 1ml no matter how much air was present in the tip or how long the tip is.

Now... for reading you turn the syringe upside down and read from 1ml back up the scale to 0. Since this will be pure liquid you'll get the remainder from 1ml.

Hope this makes sense.
 
<a href=showthread.php?s=&postid=14030829#post14030829 target=_blank>Originally posted</a> by EddieJ
Now you fill the the same syringe with to the 1.0 ML mark, but this time you have an air pocket occupying .3 ML of the syringe. You depress the plunger and it travels to .1 again. This time you have dispensed .6ml of reagent because .3 of the volume was filled with air.
Click to expand...

If you start with the plunger starting at 1.0 and the air bubble is X and you depress to .2 and the bubble is still X then the amount added is:

(1.0 - X) - (.2 - X) = .8 - X + X = .8

So, as long as you use the same reference, the size of the bubble does not matter. However, if you run over more than 1 full syringe, you will have to add the result of each. In other words, record the result for a syringe reading of 0. Fill the syringe back to 1.0 and continue, record that result and then add the two.

Todd
 
Now that the bubble is out of the way...

I just performed 4 tests

LaMotte 8.3
Hagen 7.9
Salifert 11.2

Then I used the included reference sample with the Salifert and it was dead on using the Salifert Kit (7.8 dkh)

I then performed the test on the reference sample with the LaMotte and it came out

5.7

So, from the looks of it the Hagen and the LaMotte are WAY off.. They are approaching a year that I have had them, so who knows how old they are but it appears I have been running my tank at 11 dkh over most of the last year. Funny how 2 kits are in the same ballpark. Think I might grab a new API alk kit and see where it comes in at.

I have been running fully saturated kalk at around a gallon a day (ATO) and was wondering why I still needed to dose 50ml two part daily as well. I still may need to keep that going as the alk readings were steady during the time I was using the LaMotte. I am going to ease back on the 2 part and see where it settles in at.

Thanks for everyone's help in the bubble caper !
 
API will get you within 1 dkh providing it is less than a year old. I have had good luck with this kit.

As far as the Salifert, I have been using it for years. The liquid level usually ends up about .76 or so as long as you draw slowly. As others have said this is normal.

I have not had good luck with Hagen or LaMotte for different reasons, so I think at this point, I think the Salifert is giving you pretty good results.

Aside from all of that gibberish, if your alkalinity is between 7 and 12 dkh and is stable, I would not lose too much sleep over it. :)
 
If you mix up a small batch of your Reef Crystals salt mix to a salinity level at 1.0264, using a properly calibrated refractometer, then your alk. reading for this mix should be about 12 dKH. This would be the simplest way to test which kit is accurate. :)

You could test your other kits (calcium & magnesium) and compare the results in a similar manor for approximate accuracy also.

http://www.reefcentral.com/forums/showthread.php?s=&threadid=1287118&perpage=25&pagenumber=1
 
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If I were to do this and my salinity is at 1.240 could I change right to 1.0264 or is it to sudden of a change for to much and It will only be 10% water changes each week
 
All you have to do is mix up enough for a 5% water change and then run your tests. After that add more water and enough salt mix for your 10% water change to what salinity level you desire.
 
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