DIY alkalinity standard

[trevorhiller]

I do not know if this standard is a curate for the Hanna. See this post earlier in the thread:

DIY alkalinity standard

For folks who may want to evaluate the accuracy of their alkalinity test kits, here are two suggested ways to do it. One is DIY and one is a mostly commercial standard with one DIY step. Method 1 Standard solutions could be made with sodium bicarbonate, but it can be hard to be sure it hasn't...

www.reef2reef.com

Don't know how I missed that! Thanks for bringing it to my attention

 

[Randy Holmes-Farley]

Randy, can Soda ash be substituted for method 1 here?

The recipe uses soda ash (sodium carbonate). Bake it first to be sure it is dry and is not partly bicarbonate.

 

[Miami Reef]

Dissolve the 10 grams of powder in 1.0 liter (1000 g) of RO/DI or distilled water. The more accurate you are with this measurement of water, the more accurate the standard will be.

Just making sure, for the first step, the volume will be more than 1,000mL when the powder is dissolved into the water, right?

 

[Randy Holmes-Farley]

Just making sure, for the first step, the volume will be more than 1,000mL when the powder is dissolved into the water, right?

Probably, but if you go by mass there is no error from this effect, and at most the volume change is a few mL so less than a 1% deviation from the mass based answer.

 

[Miami Reef]

Probably, but if you go by mass there is no error from this effect, and at most the volume change is a few mL so less than a 1% deviation from the mass based answer.

What do you mean by ”by mass?”

I plan to use a 1L volumetric flask.

 

[Randy Holmes-Farley]

What do you mean by ”by mass?”

I plan to use a 1L volumetric flask.

When looking closely at my directions:

Remove 15.1 grams (or 15.1 mL) of Stock Solution #1 and combine the 15.1 g with Ro/DI or distilled water to a final total mass of 1000 g or a volume of 1000 mL.

I suggest one can take the 15.1 g by mass or volume. In any case, the error will be very small. Much smaller than any hobby kit can detect, I expect.

If I were you, I'd use 1 L before mixing. It might be interesting to mix in the volumetric and see roughly what volume change one gets.

 

[Miami Reef]

When looking closely at my directions:

Remove 15.1 grams (or 15.1 mL) of Stock Solution #1 and combine the 15.1 g with Ro/DI or distilled water to a final total mass of 1000 g or a volume of 1000 mL.

I suggest one can take the 15.1 g by mass or volume. In any case, the error will be very small. Much smaller than any hobby kit can detect, I expect.

If I were you, I'd use 1 L before mixing. It might be interesting to mix in the volumetric and see roughly what volume change one gets.

I did it adding the 10g to the 1L. The volume went slightly above the volumetric line.

I got a perfect 8dKH result with my titration. I’m happy with the results.

 

[Randy Holmes-Farley]

I did it adding the 10g to the 1L. The volume went slightly above the volumetric line.

I got a perfect 8dKH result with my titration. I’m happy with the results.

Sounds good!

 

[Danchik]

Method 2.
For those who do not want a pure DIY, but want a highly accurate standard, you can start with a premade solution of 0.01 N sodium hydroxide, such as this one from amazon for $16.45:

LabChem LC242001 Sodium Hydroxide Solution, 0.01N (0.01M), 500 mL Volume

As it arrives, this solution contains 10 meq/L of alkalinity, or 28 dKH. You could use that without dilution with a test kit, but will typically need a lot of titrant to reach the endpoint, wasting the titrant.

If you take 250 mL of this fluid and 750 mL of RO/DI water (or any volumes that are a 1:3 ratio), you will have a fluid that is 7 dKH and is ready for titration kit testing.

Hello @Randy Holmes-Farley,
I would like to ask you if you could recalculate the "dKH" for "Method2" with a different value of 8 dKH, because I'm afraid I'll make a mistake...(
If:
Sodium Hydroxide Solution, 0.01N, 500 mL Volume

Thank you!

 

[Randy Holmes-Farley]

Hello @Randy Holmes-Farley,
I would like to ask you if you could recalculate the "dKH" for "Method2" with a different value of 8 dKH, because I'm afraid I'll make a mistake...(
If:
Sodium Hydroxide Solution, 0.01N, 500 mL Volume

Thank you!

I'm confused. I gave a recipe for 7 dKH. Why would you want or need to test 8 dKH?

 

[Danchik]

I'm confused. I gave a recipe for 7 dKH. Why would you want or need to test 8 dKH?

Since my average value in the aquarium is =>8 dKH, I would like to get closer to this value
I understand that 7 dKH will do, but it is further from my average value

 

[Randy Holmes-Farley]

Since my average value in the aquarium is =>8 dKH, I would like to get closer to this value
I understand that 7 dKH will do, but it is further from my average value

I do not think that is a significant concern for a test that is linear with titrant added. However, if you feel you want 8 dKH, use 286 mL mL of 0.01 N NaOH diluted with RO/DI water to 1 L total final volume.

 

[Danchik]

I decided to just attempt to make another batch of solution rather than worrying about how I had messed up. This time forewarned with the fact that I am using a 0.1N standard, I mixed 25ml of 0.1N with 1L of RODI. On my first test of the new standard, I got some really low reading (around what I had before). I re-tested, but with better light and I stopped as soon as the test changed to purple. When I compared the chart, 7.0 dkh. Yay! What I realized is that I had been going too far past the colour change. I was shooting for pink, but the change from blue to purple seems to be the correct point.

I went back and re-tested my tank water, being more careful to nail the colour shift, and got a reading that matched my automated tester, which is what I have been trying to validate.

Now I can crank up my CaRx effulent being assured of the numbers I am targetting. I was able to use the 7.0 dkh standard to not only validate the test, but to validate the tester (me). So a success all around.

Dennis

Ya, I should have been more clear. Going past the point of colour change explained the difference I was trying to validate between the Salifert and my Alkatronic. My Alkatronic was reading 7.2x dkh and my (incorrect) manual testing was showing 8.0 - 8.3 dkh.

I am not sure how I flubbed the first manual test that came out close to the bad standard, but with the various flasks and beakers I had strewn across the kitchen counter, I found a way

Thanks for your help.

Dennis

Hi @Dennis Cartier,
I'm confused, or I don't understand something...

In the instructions for Salifert, it is stated that the end of the titration reaches the pink color, from: blue>purple>pink!

And for some reason you chose the end of the titration as "purple"... These are different values at the output (dKh)!? ...Because the numbers in the calibration solution seem to have coincided

Most likely, the data for making the calibration solution are incorrect... unless you have a manufacturing error.

-----------------------------------

Interestingly, I also repeated myself with Sodium Hydroxide Solution, 0.01N

I ordered the "Sodium Hydroxide Solution, 0.01N" from the laboratory with the result of the quality analysis.
And I got 8.4dKh (to pink color) and according to the instructions from the 1st post it should be 7.0
By the way, when titrated, at 7.0dKh I still had a blue color!

I have already made the calibration solution 2 times and for some reason the same numbers are obtained...

 

[Randy Holmes-Farley]

Hi @Dennis Cartier,
I'm confused, or I don't understand something...

In the instructions for Salifert, it is stated that the end of the titration reaches the pink color, from: blue>purple>pink!

And for some reason you chose the end of the titration as "purple"... These are different values at the output (dKh)!? ...Because the numbers in the calibration solution seem to have coincided

Most likely, the data for making the calibration solution are incorrect... unless you have a manufacturing error.

-----------------------------------

Interestingly, I also repeated myself with Sodium Hydroxide Solution, 0.01N

I ordered the "Sodium Hydroxide Solution, 0.01N" from the laboratory with the result of the quality analysis.
And I got 8.4dKh (to pink color) and according to the instructions from the 1st post it should be 7.0
By the way, when titrated, at 7.0dKh I still had a blue color!

I have already made the calibration solution 2 times and for some reason the same numbers are obtained...

You might find this thread worth reading:

Alkalinity titration endpoint pH & Salifert endpoint color

TL;DR: The endpoint pH is 4.41, and the endpoint color is that "lavender" color I've been telling people about. Over the years, there have been many threads on R2R and other forums debating a couple of basic details relevant to testing for alkalinity in reef aquaria. One of the most...

www.reef2reef.com

 

[TCoach]

@Randy Holmes-Farley is there a way to do this using Kalkwasser? Sodium hydroxide is nasty stuff and I’d have to order it. I have lots of Kalk powder already here. (BRS Kalk if that matters)

Thanks,
-Chris

 

[Randy Holmes-Farley]

@Randy Holmes-Farley is there a way to do this using Kalkwasser? Sodium hydroxide is nasty stuff and I’d have to order it. I have lots of Kalk powder already here. (BRS Kalk if that matters)

Thanks,
-Chris

While possible, it’s a lot harder to be sure it is dry and adequately pure and has not reacted with CO2 to any important degree, yes.

You also cannot use the dilution step as outlined, so have to weigh small amounts accurately.

 

[taricha]

While possible, it’s a lot harder to be sure it is dry and adequately pure and has not reacted with CO2 to any important degree, yes.

What if you skipped the known mass into known volume step and went straight to the use of a saturated solution?

Saturated, clarified limewater should have an alkalinity of 114 dKH at 25C and 118 dKH at 20C. Doing a dilution to reasonable tank water Alk for a standard at the time of measurement might work reasonably well?
(I've never tried it)

 

[Randy Holmes-Farley]

What if you skipped the known mass into known volume step and went straight to the use of a saturated solution?

Saturated, clarified limewater should have an alkalinity of 114 dKH at 25C and 118 dKH at 20C. Doing a dilution to reasonable tank water Alk for a standard at the time of measurement might work reasonably well?
(I've never tried it)

Yes, I was thinking about that as a possibility. One needs to be sure it is totally settled of any small solids, but at 25 deg C, saturation is exactly 0.0204 M, or 40.8 meq/L = 114 dKH.

 

[taricha]

Saturated, clarified limewater should have an alkalinity of 114 dKH at 25C and 118 dKH at 20C. Doing a dilution to reasonable tank water Alk for a standard at the time of measurement might work reasonably well?
(I've never tried it)

I'd been meaning to try this, since I always have a kalk bucket around. And I got new alk kits from Red Sea (my normal) and Salifert (hadn't used it before) - so I wanted to see how well saturated clarified kalk worked for me as a standard.

I sampled my kalk bucket from below the crust and diluted it with distilled water to make two standards - 7.0 dKH and 11.0 dKH.
I measured them against a sulfuric acid standard + pH meter.
Seems like it worked pretty well.

The Blue data is vs acid standard, very close to theory (black line).
The yellow and red are my new salifert and red sea kits.

I'm not sure why +-1dKH discrepancies are so common between different alk kits (not that it's huge, it's like 10% ) but I'll simply note that yes, +-1dKH discrepancies seem pretty common between kits.

 

[Randy Holmes-Farley]

I'd been meaning to try this, since I always have a kalk bucket around. And I got new alk kits from Red Sea (my normal) and Salifert (hadn't used it before) - so I wanted to see how well saturated clarified kalk worked for me as a standard.

I sampled my kalk bucket from below the crust and diluted it with distilled water to make two standards - 7.0 dKH and 11.0 dKH.
I measured them against a sulfuric acid standard + pH meter.
Seems like it worked pretty well.

The Blue data is vs acid standard, very close to theory (black line).
The yellow and red are my new salifert and red sea kits.

I'm not sure why +-1dKH discrepancies are so common between different alk kits (not that it's huge, it's like 10% ) but I'll simply note that yes, +-1dKH discrepancies seem pretty common between kits.

Very interesting, thanks for doing it!

I presume you know it, but others may not. The temperature of the kalkwasser is important, and it is critical to have no cloudiness or solids enter the test sample.