Salifert Kh testing question

glb · Apr 13, 2015

I've been using a hanna checker which I love but the reagent is on back order from Amazon Prime, so I bought a Salifert test until it comes in. Question: do you keep dosing until the water changes colors and stays changed or just until it quickly changes then returns to the original color? The reason I ask is that my Salifert tested at 14k and the hanna tested at c 10.4. There's no way my Alk is 14 so I think it's a test error. Can someone help me with this test?

glb · Apr 13, 2015

Ok I think I read it wrong. I tested again today and the correct reading seems to be 8.5kh. I just noticed that my Hanna checker reagent expired at the end of last year. It measured at about 10.4kh. Which should I trust?

Randy Holmes-Farley · Apr 13, 2015

When two kits disagree, there no easy way to tell which (if either) is accurate.

glb · Apr 13, 2015

Yikes.

JimWelsh · Apr 14, 2015

I've used both Salifert and also the Hach method with their reagents. I find both methods to be very, very similar. Hach has pH buffers you can use to help determine the correct endpoint color. It is what I would describe as a nice lavender, somewhere between the blue/green of the initial color and the very pink color you get when you have passed the endpoint.

What I have just described is similar to what Habib from Salifert has described elsewhere. Not sure if this link is OK or not in this forum, but here goes nothin': Salifert Alkalinity Test Kit - Reef Central Online Community

Randy Holmes-Farley · Apr 14, 2015

Additionally, titration kits are typically done when the color stays at the endpoint color, not when it changes quickly back to the original color.

Z06-Hec · Apr 14, 2015

to answer the question about the color changing, when your are adding drop by drop you should be swirling the tube after each drop. Once you get to the point you see the liquid change and then when you swirl it goes back then it is not changed yet. Once it changes and stays changed then you read how much is left. it usually will hit a purple-ish color before it hits its orange-pink state 1-2 drops after.
sometimes its harder to tell depending on the lighting in the room.
I like to lay a flash light on the table pointed at the tube and when i see it change to be sure i hold it up to the natural light as well.
I have compared my salifert to reef master by instant ocean and they generally are really close, maybe off by 1 point. Never had the Hanna checker though.

Randy Holmes-Farley · Apr 14, 2015

FWIW, you can also monitor the endpoint by pH, if you have trouble with the color. . It is done at about pH 4.2

GlassMunky · Apr 14, 2015

glb said:
Ok I think I read it wrong. I tested again today and the correct reading seems to be 8.5kh. I just noticed that my Hanna checker reagent expired at the end of last year. It measured at about 10.4kh. Which should I trust?

I would think the test kit that is in date would be more accurate, but thats just a guess.
Personally i think the best thing to do when 2 test kits disagree is to get a friend or lfs to test your water with one of their kits as another point of data and see if that is close to either of your original test kits. whichever reading that comes closest to is probably the correct number. (Or close)

Z06-Hec · Apr 14, 2015

Randy Holmes-Farley said:
FWIW, you can also monitor the endpoint by pH, if you have trouble with the color. . It is done at about pH 4.2

Sorry, curious to understand what you mean here?
Test the ph of the water hes testing and it should read 4.2 ?

glb · Apr 14, 2015

Randy Holmes-Farley said:
FWIW, you can also monitor the endpoint by pH, if you have trouble with the color. . It is done at about pH 4.2

Very cool. I'll check it out. As soon as my hanna reagent comes I'll go back to it but for a number as important as Alk, I'm glad I have two kits now.

Randy Holmes-Farley · Apr 14, 2015

Z06-Hec said:
Sorry, curious to understand what you mean here?
Test the ph of the water hes testing and it should read 4.2 ?

An alkalinity titration adds acid until the pH is about 4.2. That's where the color "should" be changing in such a test (like the Salifert kit), but it may not be exactly right due to the inability to get the dye(s) to change color exactly at the pH you want.

This has more:

A DIY Alkalinity Test: By Randy Holmes-Farley - REEFEDITION

glb · Apr 14, 2015

Today Hanna checker was 10.9kh and Salifert was 8.9. New hanna reagent on the way. Since both numbers are normal I'm not going to worry about it.

Randy Holmes-Farley · Apr 14, 2015

glb said:
Today Hanna checker was 10.9kh and Salifert was 8.9. New hanna reagent on the way. Since both numbers are normal I'm not going to worry about it.

That's a good way to think about it.