salifert alkalinity test

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Nick Rose

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For the past 6 months I have been using the API Alk test. Today I started using the Salifert test kit and noticed the numbers are off. The API says 8-9 (it turns a slight yellow at 8 but a bright yellow at 9) and the Salifert reads 7.7. I'm going by Billy Pipes video of having the water line at .85 when the plunger is at 1ml. But when I have the most air gap where the water line is near .81 I get a Alk reading near 8.6. This was being tested on my newly mixed salt water which I use Aquavitro Salinity which should be mixing between 8.96-10.64. So which test kit should I trust and how big should the air gap be, should it be .15 or .19? The other numbers of the salt was 1.026, 430, 1380, 79F. The Ca/Mag was with Salifert with a .15 air gap. I've been dosing my tanks thinking they were at 9 so before I starting dosing to bring it up from the 7.7 I want to make sure the right test method.
 
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That doesn’t answer the question. Depending on how you pull the plunger you can either have a large air gap or small air gap which gives different results. With the small air gap I got 7.7 or lower and with the bigger air gap I got 8.6.
 
Yes it does answer the question. The size of the air gap doesn't matter, as long as you don't deliver air during the titration. Get over the air gap size issue; it is a red herring. You only care about the amount of reagent delivered. That is measured as the difference between the plunger measurement at the beginning of the titration and the measurement at the end of the titration.

EDIT: If the air gap size difference gives you different readings on the same sample, then perhaps you are mis-reading the syringe. You are reading from the bottom of the black plunger, and not reading the meniscus at the bottom of the air gap, correct?
 
Last edited:
Did u read the instructions? I think some or the old test require 4drops of the kh-ind reagent. But it seems some require only 2 drops. Now i need to read my manual again when im home :(
Billy pipes video was 4drops
 
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Mine was 4 drops and it’s a new test kit. But I’ve seen that on here and it seems like it doesn’t matter if it 4 or 2 drops.
 
I've just been through this here:
https://www.reef2reef.com/threads/s...y-below-api-yellow-which-one-is-right.604765/

I ended up getting roughly the same readings with two Salifert test kits and deciding to trust Salifert and not my API test. ... do your corals look happy? I'd just pay attention to the inhabitants, they'll probably tell you if something is way off.

I'm still adjusting my (k)Alk dosing but being very cautious with it just to be safe. I'd rather err on the side of not dosing enough than too much as my corals all seem to be fine.
 
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Yes the majority of the corals look happy. I do have two Acans that I bought in April that aren’t as happy but I believe it deals with flow/light. I did just buy a Birdsnest on June 21st and it looks really happy.
 
@JimWelsh So you were right. I don't know why last night it was giving different results. But today I did it 5 different times with different air gaps and they all matched each other. With that resolved there is still the question of the Salt mixing at a lower Alk then its labeled to. I guess I will start a new thread dealing with that.
 
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The salifert kit has the option of doing a lower resolution test which uses 2 drops of the first reagent. It also uses less water i believe.

But if your syringe is pushed all the way down when you initially draw up the solution the airgap shouldnt be a different size(at least my airgap is consistently the same size. The plastic tip that pushes onto the syringe is there to create smaller drops. That tip being there means you are going to have an airgap.
 
I’ll just add that the amount of indicator dye in an alk titration should also not make an appreciable difference. The amount added is not important. It is just there to indicate pH by color.
 
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Should I start another thread about the Salinity salt not mixing to the Alk posted on the bucket. I mixed 10 gallons to 1.026 at a temp of 78. I tested it 8 hrs later and the Alk was 7.7 and the other parameters were as listed on the bucket. Today I mixed up a one gallon jug and the Alk was 10. Yes I mixed the salt before scooping so it was mixed.
 
I used to think the air gap mattered as well. It does not and there is no difference in final results. Salifert tests do change from time to time as well. From how many drops of reagent to use as well as how to view color results (from top of from the side). You need to read the instructions that came with your individual kit.
 
Nick Rose said:
Should I start another thread about the Salinity salt not mixing to the Alk posted on the bucket. I mixed 10 gallons to 1.026 at a temp of 78. I tested it 8 hrs later and the Alk was 7.7 and the other parameters were as listed on the bucket. Today I mixed up a one gallon jug and the Alk was 10. Yes I mixed the salt before scooping so it was mixed.
Click to expand...

Yes, that’s a good idea
 
Nutramar Foods
JimWelsh said:
Yes it does answer the question. The size of the air gap doesn't matter, as long as you don't deliver air during the titration. Get over the air gap size issue; it is a red herring. You only care about the amount of reagent delivered. That is measured as the difference between the plunger measurement at the beginning of the titration and the measurement at the end of the titration.

EDIT: If the air gap size difference gives you different readings on the same sample, then perhaps you are mis-reading the syringe. You are reading from the bottom of the black plunger, and not reading the meniscus at the bottom of the air gap, correct?
Click to expand...
The air gap “is a red herring”. That is a classic comment imo. Sometimes we can’t get past the obvious. Kind of sums up the world these days.
 

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