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.
