How many grams baking soda per 1 gallon of distilled water for 4dkh? - The Planted Tank Forum
Old 12-08-2014, 06:45 PM Thread Starter
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How many grams baking soda per 1 gallon of distilled water for 4dkh?

Hello all, I've tried looking through old threads and I've come up short.

Just looking how many grams of baking soda I need to add to 1 gallon of distilled water to reach 4 dkh for my drop checker solution.

I have an accurate scale to do this.

Thanks!

Edit: Beh I'll just do the math. Let me know if I am wrong:

NaHCO3 = 84 g/mol
1 gal = 3.76 L
1 dkh = 17.8 ppm as CaCO3

4 dkh = 71.2 ppm

CO3 is (60 g/mol) / (84 g/mol) which is 71.4% of NaHCO3

We need mg/L which is ppm

To get 71.2 ppm of NaHCO3 in 3.76 liters (1 gallon) we need 71.2 mg/L * 3.76 L =~ 264 mg NaHCO3

However, CO3 is just 71.4% of the whole, so need to multiply result by 1.286

264mg * 1.286 =~ 340mg of NaHCO3 to reach a total of 71.2 ppm CO3

I'm a physicist by trade, but I think this is correct based on my gen chem classes five years ago

Last edited by Positron; 12-08-2014 at 07:20 PM. Reason: doing the math
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Old 12-08-2014, 06:54 PM
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Slightly over 0.454 grams.

Most folks create a 40dKH solution first, and then dissolve that 1:9 with distilled water to create 4 dKH, just to make the scale resolution less of a problem. Use of metric system volumes of liquids also results in more even numbers than gallons does.

Last edited by mattinmd; 12-08-2014 at 06:54 PM. Reason: removed stray "m." from text...
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Old 12-08-2014, 07:23 PM Thread Starter
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Quote:
Originally Posted by mattinmd View Post
Slightly over 0.454 grams.

Most folks create a 40dKH solution first, and then dissolve that 1:9 with distilled water to create 4 dKH, just to make the scale resolution less of a problem. Use of metric system volumes of liquids also results in more even numbers than gallons does.

Hmm can you tell from my math what I'm missing, Matt? Thanks.
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Old 12-08-2014, 07:48 PM
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Old 12-08-2014, 08:22 PM
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Quote:
Originally Posted by Positron View Post
Edit: Beh I'll just do the math. Let me know if I am wrong:

1 dkh = 17.8 ppm as CaCO3
That's as CaCO3..

1) your calculations are assuming 17.8mg/l of CO3 to make one degree. But it takes 17.8mg/l of CaCo3, or 10.7 mg/l CO3.

2) your calculations also assumes that one molecule of bicarbonate (HCO3) contributes the same amount of KH as a plain carbonate (CO3). Carbonate is a -2 anion, and is twice as strong as bicarbonate here. (ie: the bicarbonate is already half-neutralized by the extra hydrogen).

Thus it takes twice as much bicarbonate to raise the KH as much as carbonate does.

http://en.wikipedia.org/wiki/Carbonate_hardness

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Old 12-08-2014, 09:14 PM Thread Starter
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Excellent, thanks for the clarification.
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