How to make a 4dkh solution

  1. Dissolve 1 tsp (6 grams) of sodium bi-carb into 1 litre of distilled water. 
  2. Take 10mL of this solution and dissolve it further into 490mL of distilled water.

You now have a solution with carbonate hardness of 4 degrees.

This can be used in a drop checker to estimate visually what the concentration of CO2 is in your aquarium water.

You can store the remaining solution in an air tight container out of direct sunlight for several months.