DIY alkalinity standard

Dkeller_nc

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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
Glad to hear it worked!

One comment about what you described. With the Salifert test, going way past the end-point would increase the apparent alkalinity, not decrease it. I'd double check to make sure that you're correctly interpreting the syringe readings with respect to Salifert's alkalinity chart.
 
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Dennis Cartier

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Glad to hear it worked!

One comment about what you described. With the Salifert test, going way past the end-point would increase the apparent alkalinity, not decrease it. I'd double check to make sure that you're correctly interpreting the syringe readings with respect to Salifert's alkalinity chart.

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 :rolleyes:

Thanks for your help.

Dennis
 

Dkeller_nc

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Ah - that makes more sense. Glad it worked out for you.

An amusing side comment to your quip about having various beakers and flasks on your counter - it wouldn't shock me if my neighbors think I'm doing something nefarious in my kitchen, since they'd see me holding various pieces of scientific glassware to the light on a regular basis to check the volume. And, of course, in the general public's mind, if you have glassware from a laboratory in your home, you must be Walter White. ;)
 
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Erin1971Texas

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This is what I did, and the results I got. Using Not the Best Scale.....

2020-04-29_DIY-AlkReferenceMethod1-a.jpg




I do hope your oven was set to 400 degrees *fahrenheit*. Thank you for the pictorial :)
 

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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 begin to absorb moisture and/or decompose into sodium carbonate.

Thus my suggestion is to start with sodium carbonate, and bake it yourself to be sure it is dry. If not dry, the weight of the water will make the standard less potent than you expect.

To fully dry sodium carbonate before use we will bake it in a home oven.

Preheat the oven to about 400 deg F.

Spread about a quarter cup of sodium carbonate on a pyrex casserole dish or a roasting pan. You want CO2 and H2O gas to readily escape from it, hence the spreading out.

Place it in the oven and leave it there for 60 minutes.

Remove and cool the dish. Don't place it right near a pot of boiling water, you do not water it reabsorbing moisture.

Weight out 10.0 grams of the dry solid powder (scale the whole recipe down if your scale cannot weigh 10 grams). This 10 grams contains 0.0943 moles (94.3 mmoles) of sodium carbonate. Each carbonate contributes 2 units of alkalinity, so this 10 grams contains 2 x 94.3 mmoles = 189 milliequivalents of alkalinity.

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.

This solution has an alkalinity of 189 meq/L, which equals 528 dKH. Call this stock solution #1.

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.

This final solution will contain 189 meq/L x 0.0151 L = 2.86 meq in one liter = 8.0 dKH.

This final solution can be used to test a titration test kit for total alkalinity.

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.

If anyone notes a math error in either recipe, please let me know :)

Happy Reefing

In Method 1 using sodium carbonate is there a shelf-life for either solution 1 or the final solution?

A liter of either ought to go a along way and I am just curious how long it can be stored?

Thanks
 
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Randy Holmes-Farley

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Syntax1235

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I used brs soda ash to make the solution. I was having trouble figuring out my tank dkh after changing test kit brands from Red Sea to Salifert…. Red Sea was giving me a reading of 7.0 and Salifert 8.0, too much of a discrepancy.

I made the solution as close to the directions as possible and ran alk tests from each brand….. Salifert came in at 8.15 and Red Sea was 7. Salifert will be the test kit I use for in perpetuity.

Thanks @Randy Holmes-Farley
 
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Randy Holmes-Farley

Randy Holmes-Farley

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I used brs soda ash to make the solution. I was having trouble figuring out my tank dkh after changing test kit brands from Red Sea to Salifert…. Red Sea was giving me a reading of 7.0 and Salifert 8.0, too much of a discrepancy.

I made the solution as close to the directions as possible and ran alk tests from each brand….. Salifert came in at 8.15 and Red Sea was 7. Salifert will be the test kit I use for in perpetuity.

Thanks @Randy Holmes-Farley

You're welcome.

Happy Reefing. :)
 
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Randy Holmes-Farley

Randy Holmes-Farley

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Thanks RHF for this. I made this today and checked my Hanna Checker and got a result of 6.8. Not quite as accurate as I had hoped.
I do not know if this standard is accurate for the Hanna. See this post earlier in the thread:
 
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