Here is the information that I found on how to make a KH standard.
I did a lot of searching and this seems to be the correct way to make a KH standard solution. Thanks, Tom Barr, Randy Holmes and Jose from helping to clear this up.

After I got all of the supplies in to make the KH standard I went to this thread and got Tom’s instructions.

KH reference methods, the drop checker and the pH probe adaptations

>>>Cooked/baked baking soda: 400F for 45 min.
Use about 2x what you think you need.

10 grams may yield 6 grams after dehydrating.
Sometimes 8 if you live in drier areas.

I add 4.99 grams to 5 liters of DI water.
This makes 40KH.

Add 10mls of this to 90 mls of DI water to make a 4KH solution.

Regards,
Tom Barr<<<

I was going to make my standard 5 dKH instead of 4 dKH, so I went to the KH calculators below to see how much baking soda (sodium bicarbonate) I would need to add. That’s when I first found out that something was wrong because the calculators gave different results.

I made larger samples and I was always planning on making larger sample sizes as Tom had suggested but just for comparison purposes I was calculating how much sodium bicarbonate to add to 1 liter of water to get 5 dKH.

The first calculator said to add:
100 mg from Jose’s calculator / 'Reef Chemistry Calculator FV'
(Note the above calculator now shows the correct amount of sodium bicarbonate to add 149.9 mg – it was changed due me asking about the difference. This is the calculator to use it is accurate)

The second calculator said to add:
125 mg from web calculator / CNYKOI - Alkalinity (KH) calculator

The second problem I ran into was the heating of the baking soda, I had read on the web site below that if you heat sodium bicarbonate at 392 degree's F that the sodium bicarbonate changes to sodium carbonate. This was causing more problems because you could end up with all sodium carbonate or a mixture of sodium bicarbonate and sodium carbonate.

General Chemistry Online: FAQ: Introduction to inorganic chemistry: What happens when sodium bicarbonate is heated?


At this point I started going to the chemistry/lab forums looking for answers and while they helped some they didn’t give me the information that I was looking for.

The real help came from the forum called “The Reef Chemistry Forum” over at Reefcentral.com
Randy Holmes and Jose really helped clear things up, below is the link to the discussion. If you have any doubts about there numbers check out Randy’s resume of work.

Reef Central Online Community - Heating baking soda

So here are the basics of making the KH standard. I have tried both the sodium bicarbonate and sodium carbonate with these numbers and everything comes out just right.

The weights I posted here is the amount of sodium carbonate or sodium bicarbonate needed to make a 4 dKH and a 5 dKH standard in one liter of water. I just did it this way because it was easier for me to compare. Although the numbers are accurate I made my sample sizes larger as Tom has suggested for better accuracy.

To make the KH standard solution.

Use distilled water

add baking soda (sodium bicarbonate) or sodium carbonate
-

• sodium carbonate can be bought from a lab supply
• -the sodium carbonate anhydrous is 99.5% pure, compared to baking soda which is 97% pure. The sodium carbonate anhydrous would give you a little more accurate sample.

This is the calculator to use,

• -again it was wrong but Jose has changed it and it works great.
• -you can select to use either sodium bicarbonate or sodium carbonate and it will give you the correct weights
• -when using sodium carbonate anhydrous the calculator calculates this as 100% -the sodium carbonate anhydrous that I bought was 99.5% so I needed to multiply the weight the calculator gave by .005 to get the correct amount to add. So if you buy your own sodium carbonate anhydrous keep this in mind and calculate accordingly
• -The calculator rounds everything up because it was made for calculating aquariums not small samples. To get accurate weights just add some zero’s to the sample size.
• For example: when I enter in 1 liter of water and 5 dKH of baking soda it gives me a weight of .1 grams of baking soda to add. I want a more accurate amount to add so I increased the water from 1 liter to 1000 liters and I now get a weight of 150 grams. By doing this I know to add .15 grams instead of .1 grams

weight of baking soda to add for standards

• -1 liter of distilled water with a 5 dKH .15 grams (actually .14994)
• -1 liter of distilled water with a 4 dKH .12 grams
• -5 liters of distilled water with a 40 dKH 6.00 grams

Bill