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Grumble *multiple test kits* & homemade 4dkh solution

2499 Views 4 Replies 2 Participants Last post by  sewingalot
I bought Hagen test kits recently and I get 4dkh every time after making this solution:

However, API shows the solution to be 2dkh. Then, to make it more confusing, I take out my old SeaChem (like six months old) and it reads 5dkh.

Which is more reliable - the formula on the link, the Hagen test, the API, or the SeaChem?

What's funny in this frustation? That my first batch was made with city water since my dear husband "refilled" the distilled water. "Water's water, right?" That's his nonchalant response to my inquiries. :tongue:
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I very carefully made my 4 dKH solution, using a certified lab standard carbonate solution, then a year or so later, tested it with my API test kit, and got 5 dKH. I had been very trusting of my KH test kit, figuring that of all the test kits, this one would always be reliable (because I wanted to believe that, I guess)

You could try to calibrate the KH test kits using the "kitchen utensil" type of method I posted in the sticky on calibrating test kits. That might give you at least an idea about which test kit, if any of them, comes closest to being right.

Another test kit I just know has to always be right, no doubts at all, because I want that to be true too, is the pH test kit.:biggrin:
Hoppy said:
KH Test Kit

First, buy one gallon of distilled water from your local grocery store. Set a reasonably accurate thermometer on the kitchen counter near where you will be working. Get an empty plastic bottle that contained bottled non-carbonated drinking water. Wash the bottle with plain tap water a few times, then rinse a couple of times with distilled water.

1. Add enough distilled water at near room temperature, or slightly above, to the bottle, to get it about 2/3 full, or at least 1 cup of water.
2. Add about 5 teaspoons or more of bicarbonate of soda, sodium bicarbonate, baking soda to the water and gently swirl it around a few seconds.
3. Make sure there is still some undissolved baking soda at the bottom of the bottle.
4. Squeeze the bottle slightly to expel some of the air, and cap it to seal the bottle.
5. Leave it beside the thermometer for a few hours, gently swirling it a few times during that time. Make sure there is always some undissolved baking soda left at the bottom of the bottle. (Vigorous shaking of the bottle will cause some of the carbonates to break down, leaving CO2.)
6. Record the thermometer reading in degrees Celsius.
7 If the temperature is 18 degrees, you will need 1.5 ml of that water, at 19-20 degrees you will need 1.4 ml, and at 21 degrees you will need 1.3 ml.
8. Measure 2 cups of distilled water into a very clean bottle that can be capped.
9. Use a cleaned syringe, that has been rinsed with distilled water, to suck up from well under the water surface of the baking soda saturated water more than 2 ml of water. (Make sure you don’t suck up any of the undissolved baking soda from the bottom of the bottle.)
10. With the syringe “needle” under the surface of the distilled water, add the amount per step 7 of saturated solution to the distilled water, and cap the bottle. Gently swirl it to mix. You now have a bottle of 10 dKH water.
11. Add 1/2 cup of the 10 dKH water to 1/2 cup of distilled water to get one cup of 5 dKH water.
12. Add 1 cup of the 10 dKH water to 1 1/2 cups of distilled water to get 2 1/2 cups of 4 dKH water.
13. Add 1/4 cup of the 10 dKH water to 1 cup of distilled water to get 1 1/4 cups of 2 dKH water.
14. Use your KH test kit to test the KH of the 2, 4, 5, and 10 dKH samples. Record the results.
15. If the results agree with the known KH of each sample, your kit is calibrated. If not, you can make a graph of the kit readings on the “X” axis versus the known values on the “Y” axis, and use that to convert the kit readings to correct readings. Your kit will then be calibrated.
16. For future calibrations, store these standard solutions in tightly sealed bottles, labeled with their KH values.
17. For best accuracy, calibrate the KH test kit every time you use it.
Thanks, Hoppy. I read this, actually printed it out and went to work. It took me most of the evening, but the results were well worth it. Turns out the Hagen is spot on. Actually, I like this method for also making the 4dkh. It was easier not to goof up by not relying on a gram scale not being calibrated as well. :)

I am assuming once you make 4dkh that as long as it is stored in a tight container will last at least a few months. Is this correct? I have like a gallon of this stuff now.
A 4 dKH water solution should be good forever, if you can stop any evaporation from occurring. Any evaporation will raise the KH.
Awesome. So a tight lid and I never have to make it again. I only use my drop checker every few months or when I am setting up a new tank for reference, so I am set for life. Thanks!
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