Color Change in Salifert Test Kits...how do I know when it's done?

[teamlounge]

May be a dumb question but I have heard different answers so thought I would ask the community. When dripping the regent do you stop as soon as you see the color change or do you keep dripping until the color change is completely finished. The reason I ask is this could take 3 or 4 more drops which significantly changes the readings depending on what you are testing? Thx much

 

[Randy Holmes-Farley]

Depends on the kit. What type are you talking about?

In most cases, you want the color to be stable.

 

[teamlounge]

Alk, calc and mag mostly. It seems there is a couple drop process to get the new color to fully emerge. Do you stop as soon as you see the first change of color...or do you keep dropping until the newer color does not get any darker?

 

[Clownman727]

Keep dropping until final color is reached. The first color change lets you know you’re getting close.

 

[Randy Holmes-Farley]

Alk, calc and mag mostly. It seems there is a couple drop process to get the new color to fully emerge. Do you stop as soon as you see the first change of color...or do you keep dropping until the newer color does not get any darker?

Let me explain what is happening with those color changes so the answer may seem logical.

In a calcium kit, you add a dye that binds to calcium and gives a different color when calcium is bound to it compared to when not bound to it. At the start, there is less dye than calcium, so most of the calcium is free and some is bound to the dye.

As you are stepwise adding the titrant, you are adding something (like EDTA) that has a very high affinity for calcium. When first being added, it is just binding the available free calcium.

Eventually you get to the point where there is little to no free calcium left, just the calcium bound to the dye, and as you add more drops, it strips away the calcium from the dye. That causes the color to begin to change. It can take some time for the added EDTA to mix in, find a calcium/dye combination, and strip away the calcium to cause the color change. As you get to less and less dye/calcium combination left, it can take longer and longer for an EDTA to find the last few dye/calcium combos left, and so it seems to take longer for the color change.

Ideally, there is no other color change taking place once all of the dye molecules are free of calcium, so after you hit the full color change, no further change should occur.

 

[teamlounge]

ok, ty!

 

[JimWelsh]

Randy's description of a metal / chelant titration, such as the ones used for Ca and Mg is correct. As long as there is some Ca or Mg that is still bound to the dye, there will be a red-ish/purple-ish tint. You want the color change to blue to be complete (no hint of red/purple).

For the alkalinity titration, on the other hand, the color change is a more gradual one, and what you are looking for here is really in the middle of the transition from blue-green to pink. I like to use the word "lavender" to describe the correct color. Consistency is more important than matching an exact color, but the point I'm trying to make is that if you try to go to a "complete" color change with the Salifert alkalinity test, you will have overshot the endpoint, and will be reading higher than your actual alkalinity level is.

 

[Randy Holmes-Farley]

Yes, I agree with Jim. The color change need not be "complete" in an alk titration (it won't be), but should be taken to the color shade recommended by the manufacturer.

 

[Greenstreet.1]

You guys are the best thank you both made me feel confident in the way I have been using my kits. Thank you once again. MR. Randy thank you for the millionth time [emoji33][emoji23]

 

[teamlounge]

Thx for the feedback. Appreciate the insights! Still for Alk especially. 1 drop matters and it seems results can vary. I also understand that consistency is the key but am wondering if there are better, more accurate test kits out there that are not ridiculously expensive? Looking at the Hanna tester. Worth it? Running a 240g mixed reef with a tilt to SPS. thx much

 

[Randy Holmes-Farley]

Thx for the feedback. Appreciate the insights! Still for Alk especially. 1 drop matters and it seems results can vary. I also understand that consistency is the key but am wondering if there are better, more accurate test kits out there that are not ridiculously expensive? Looking at the Hanna tester. Worth it? Running a 240g mixed reef with a tilt to SPS. thx much

If you have a pH meter, you can monitor the endpoint by pH. You can do whole DIY titration very accurately that way.

Some folks do like the Hanna, but I wouldn't assume it is more "accurate" than the Salifert. It only claims +/- 0.3 dKH accuracy.

 

[teamlounge]

but I wouldn't assume it is more "accurate" than the Salifert

By accuracy I should have stated the human element. Seems the Hanna tester takes away eyeballing the color? thx

 

[Randy Holmes-Farley]

By accuracy I should have stated the human element. Seems the Hanna tester takes away eyeballing the color? thx

It replaces it with a cheap electronic eyeball.

 

[Jr'sReef]

When you get to where it starts to change color in the titration. Give it a few seconds and swirl the contents to fully dilute the whole test tube. Titration will sometimes turn a color and then once swirled turn back to original color or turn to the final product. Wait a few seconds and swirl soooo you don’t over titrate

 

[David S]

Alk, calc and mag mostly. It seems there is a couple drop process to get the new color to fully emerge. Do you stop as soon as you see the first change of color...or do you keep dropping until the newer color does not get any darker?

I can say from personal experience, as I've used the Salifert Alk, Ca and MG test kits for a number of years that the Calcium and Magnesium kits have pretty straight forward color changes. You just don't want to miss the initial color change.
For the CA it's blue. Mg is a bit trickier because the instructions indicate the color change as blue or grey, whichever is observed first. For my money, it's always been grey. The thing is to go slow once you feel you're reaching the endpoint.
The real cause for potential confusion is with the Alk test kit.
Salifert suggests to use a pink or orange (never seen orange) coloration as the endpoint, but there is an interval where there is slight but noticeable pinkish hue to totally pink. However several additional drops are needed to get from one point to the other.
So what is the answer?
I'll refer you to this thread where Jim Welsh shows the endpoint.

https://www.reef2reef.com/threads/salifert-test-kit-and-hanna-checker-results-for-alkalinity.341599/

The result may suprise you.

I can't recall the website, where there was a similar thread concerning the Salifert Alkalinity test kit in which if memory serves, Habib, the owner of Salifert, participated in. The end point described was similar to the one indicated in the link.
BTW this confounded most of the Salifert Alk test users, who were using a more definitive pinkish color for their endpoint.

Hope this helps

 

[teamlounge]

Thx very much David! Exactly what I was looking for. The biggest problem I have is with Alk testing and the subjectivity of the color change. Glad to know I am not alone. This is very helpful. Seems the Hanna checker eliminates the "human error" of color deciphering although comes with problems of it's own. Namely false reads based on cleanliness. If it reads a bit high (but is normally consistent) it seems one can figure out the pattern and go from there.

 

[David S]

Thx very much David! Exactly what I was looking for. The biggest problem I have is with Alk testing and the subjectivity of the color change. Glad to know I am not alone. This is very helpful. Seems the Hanna checker eliminates the "human error" of color deciphering although comes with problems of it's own. Namely false reads based on cleanliness. If it reads a bit high (but is normally consistent) it seems one can figure out the pattern and go from there.

Glad I was of some help.
I have never been lucky with any of the Hanna Checkers, I've owned.
Even if it was spot on from the beginning, I feel it's inevitable that they will eventually need some calibration. But 1. How would you know when it needs calibrating? and 2. how would you recalibrate it?
Answer: You can't. You would need to send it to Hanna.
I could definitely do without such "convenience".
While there is a possibility that you can get a bad batch with a Red Sea or Salifert Test Kit, it has been my experience with Salifert, especially, that they are always consistent (new vs previous test kits) in their results.

 

[esquare]

This is why i like the Red Sea kits as they put the actual colors on the little instruction card. I'm not sure how accurate Red Sea is but for me, having a picture of the actual color on the card is very helpful.

 

[BigJohnny]

I just looked at the supposed end point of the salifert result (below), how on earth is that pink/orange lol?! that is light purple or violet, like Jim Welsh says in that thread. Salifert really needs to change their instructions, I bet 99% of users are not using purple as their pink end point..........

I get that consistency is what matters most, but common. that is absolutely ridiculous imo

 

[Sleepydoc]

As I recall, Salifert includes a reference standard with their Alk test kits - your best bet is just use that to check your technique.

Salifert's inctrucions state to "continue ... until the color changes from blue/green to orange-red or pink color." I wonder where Jim is getting the end point being violet?

I've always added reagent until the color change was complete. As a practical matter, it's usually about 1 drop (0.01~0.02ml) difference between the two, and consistency is probably just as important as the actual number, so I'm not too worried.