1. Go to your local grocery store. Buy the smallest box of Arm and Hammer Baking Soda you can get. Buy a gallon of distilled or deionized water. Total cost = about $2.00.

2. Clean a glass or plastic measuring cup with distilled water. Fill it with distilled water.

3. Use a flat toothpick to scoop a tiny bit of baking soda and add it to the water. Stir with a clean plastic spoon or stir stick.

4. Use your KH test kit to measure the KH of that water. It will probably be 20-100 dKH. If it is more than 20 dKH, pour out about 3/4 of it and add more distilled water to fill the cup. Stir again and remeasure the KH.

5. The measured dKH is "K". Do the following calculation:

V = amount of "K" water to add to a cup minus V of distilled water to get a mixture which is 4 dKH.
V = [K - 4] divided by K

6. Pour out all but V of the K dKH water. Fill the cup the rest of the way with more distilled water. It will work best to use a bit more of the "K" dKH water than the calculated amount.

7. Measure the KH of that water. It should be 4 dKH. If it is more than 4, add a little more distilled water. Repeat until you get 4 dKH.