Titration based tests. When do you stop adding solution?

[bozo]

I was a biochem major in college. That was quite a while ago.

One thing I remember vividly was doing a ton of acid/base titrations in chem labs.

I remember the professor informing us that we've hit the end point of titration when the solution turns slightly pink or blue, depending on the type of titration we're running.

So when it comes to our test kits, such as Salifert ALK/CAL/MAG, when do you guys stop adding solution?

Do you stop adding solution when it completely turns dark blue or pink?

For Salifert ALK, I do cross check the titration results with a Hanna ALK tester.

So far my titration techniques are ok.

Just wondering what you guys do.

Thanks.

 

[Ron Reefman]

I use Salifert kits and I go to the end color and call that the point of correct level. But then I'll add one or two more drops just to assure myself that was far enough. But I only do the extras one out of every 3 to 5 tests.

 

[bozo]

I use Salifert kits and I go to the end color and call that the point of correct level. But then I'll add one or two more drops just to assure myself that was far enough. But I only do the extras one out of every 3 to 5 tests.

This is exactly what I do now as well.

I used titrate like how I did with those chem labs (add until slightly pink/blue), but I feel like these test kits arent as sensitive as a legit titration setup.

I wish we knew how sensitive these tests are.

 

[Randy Holmes-Farley Verified Community Expert]

For alk, you can always do it by pH, or check the pH at different colors. The endpoint is around pH 4.3, regardless of what color that is (except in Hanna).

 

[KrisReef]

My Hanna Alk meter failed to light last week end and I had to rush to the LFS to pick up a Salifert test. (So happy they had two in stock-Support your LFS!)

Anyway, I have noticed that with the color change at the titration point, if you stop and wait a minute the color will recover so another drop is needed to produce the change.

When I used to only use Salifert, I was just careful to note the amount of titrant that I used to get to the slight color change, added a drop to make sure my eyes were working properly, and most importantly, I tried to read and record the same point each time.

 

[bozo]

For alk, you can always do it by pH, or check the pH at different colors. The endpoint is around pH 4.3, regardless of what color that is (except in Hanna).

Wow. I totally forgot we always had a pH probe in the solution we were titrating into.

This is great information.

Now I'm going to try to find a thin/small enough pH probe to fit in the little Salifert container.

Thank you!

 

[bozo]

My Hanna Alk meter failed to light last week end and I had to rush to the LFS to pick up a Salifert test. (So happy they had two in stock-Support your LFS!)

Anyway, I have noticed that with the color change at the titration point, if you stop and wait a minute the color will recover so another drop is needed to produce the change.

When I used to only use Salifert, I was just careful to note the amount of titrant that I used to get to the slight color change, added a drop to make sure my eyes were working properly, and most importantly, I tried to read and record the same point each time.

This is very true in regards to waiting a few moments before adding the next drop.

Thats what we did in chem class as well.

Good point.

I use a magnetic stir rod while I'm titrating as well.

I use this contraption. It's from SR Aquaristik. Well worth it in my opinion.

 

[Miami Reef]

You can also make an alkalinity standard and see where the color endpoint ends up:

https://www.reef2reef.com/threads/diy-alkalinity-standard.714738/

 

[bozo]

You can also make an alkalinity standard and see where the color endpoint ends up:

https://www.reef2reef.com/threads/diy-alkalinity-standard.714738/

This is great information. Another article by Randy haha.

I will look into this.

Thank you!

 

[Randy Holmes-Farley Verified Community Expert]

Wow. I totally forgot we always had a pH probe in the solution we were titrating into.

This is great information.

Now I'm going to try to find a thin/small enough pH probe to fit in the little Salifert container.

Thank you!

You can do it on a large scale:

https://www.reefedition.com/a-diy-alkalinity-test-by-randy-holmes-farley/

 

[Orito]

You can do it on a large scale:

https://www.reefedition.com/a-diy-alkalinity-test-by-randy-holmes-farley/

Randy here in Brazil a local company released a kh test that's only one reagent that change the color from blue to green, I tried against salifert and it matched pretty close.

 

[Miami Reef]

Randy here in Brazil a local company released a kh test that's only one reagent that change the color from blue to green, I tried against salifert and it matched pretty close.

That looks exactly like the Red Sea Alkalinity Pro test kit reagent. :)

 

[Orito]

That looks exactly like the Red Sea Alkalinity Pro test kit reagent. :)

oh dam... never used red sea, very expensive here :rolling-on-the-floor-laughing:

 

[shrimpnreefdude]

Something I read somewhere, maybe here, all the information is merging together at this point

Is to measure the water source volume with an accurate lab grade syringe, instead of the volume lines on the tube. I thought that was a great tip.

As for the specific question, I have been going until it's a complete color change and stays changed after at least 10-20 seconds. If I swirl and it changes back, then another drop gets added.

 

[piranhaman00]

Being consistent is what matters. This hobby is about repeatability/consistency rather than actual accuracy in most cases