Easier way to measure to make drop checker solution without scales or fancy equipment - The Planted Tank Forum
 
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post #1 of 6 (permalink) Old 03-18-2010, 02:16 AM Thread Starter
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Easier way to measure to make drop checker solution without scales or fancy equipment

You'll need 2 one gallon containers of distilled water. A 12 ounce empty rinsed soda can and a teaspoon.

-Add teaspoon of baking soda to gallon of distilled water. Shake vigorously. This is your 40dkh solution.

-Take the unopened bottle of distilled water, and pour it into the soda can until the soda can is full to the opening. Discard this water.

-Fill the soda can with your 40dkh solution until it is full to the opening. Pour the soda can contents into your bottle of distilled water. This should be 4dkh now.

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Now the reasoning behind this. I measured a teaspoon of baking soda several times, and it's about 4.8 grams. Ideally we want 4.5 grams per gallon, this will be 6% over what we want.

A filled soda can contains 362 ml of liquid. Ideally we want 378 ml, but it's close enough, and about 4% under what we want, so the 6% over and 4% under should cancel each other out to within 2%. 362 ml of liquid diluted to 3.78 liters gives us about a 10:1 ratio, so 4dkh.
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post #2 of 6 (permalink) Old 03-18-2010, 04:30 AM
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Impressive! Reminds me of Die Hard (trying to get 4 L of water with only a 3 and 5 L pail).

Assuming all the measurements are correct (i.e. the baking soda is consistently 4.8g and that the filled soda can is consistently 362 mL), the final dkH of your solution would be ~4.04 dkH.

However, this is assuming that the baking soda is always the same (which will not be the case), and that the soda can is perfect

Anthony


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post #3 of 6 (permalink) Old 03-18-2010, 05:01 PM
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I think this would be accurate enough for a drop checker. But, baking soda contains a varying amount of bicarbonate per gram because it is hygroscopic, absorbing water vapor very easily. A freshly opened new box not long from the factory is likely to differ a lot from a box that has been open for a few weeks, and on the shelf in the store for several weeks before you got it. Even if your 4 dKH solution is really 3.5 or 4.5 dKH it makes little difference in the accuracy of the CO2 measurement. The major inaccuracy is in judging the color of the solution.

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post #4 of 6 (permalink) Old 03-18-2010, 09:17 PM Thread Starter
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I think all of us DIY solution makers are in the same boat until Tom figures out an alternative chemical to raise the kh. When I measured my kh in my 40 reference solution it ended up being about 35 dkh. With that many drops of kh checker solution and all the variables, who knows what it's really at.

Makes me wonder how the commercial solutions are measured.

I measured 100 grams of baking soda, and shoved it in a lab oven at 150F, making sure it did not go over 158F (the breakdown point). I waited 1/2 hour, and measured the baking soda again. It weighed 99.8 grams. I have 50% relative humidity year round and this is 5 year old baking soda. So either it takes forever to de-humidify it, or the amount of water in it is not significant...
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post #5 of 6 (permalink) Old 03-18-2010, 10:06 PM Thread Starter
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Tried baking again, spread out the baking soda thin on an aluminum sheet. Tried the same baking soda for 40 minutes. Same result. No appreciable decrease in weight. The relative humidity inside the oven should be about 9%.
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post #6 of 6 (permalink) Old 03-19-2010, 12:59 AM
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As I recall, when you bake bicarbonate of soda, you slowly transform it to sodium carbonate, which has a different percentage of carbonate in it. But, again, within the needed accuracy that isn't likely to be a problem unless carried to extreme. A drop checker is far from a precision measuring device at best, because the "reading" is proportional to 1 over 10 to the pH power for a given ppm of CO2, and reading the color of a bromothymol blue solution more accurately than +/- .3 pH isn't at all easy. Just getting a good look at the color in an aquarium is pretty difficult too.

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