Potassium is a macronutrient and at least as important as iron for a good and healthy plant growth. Therefore it is important to check the level of potassium to prevent too low levels and keep them in a healthy range ( 10-15 mg/l). The Easy-Life Potassium test is a color test with a color chart.
Optimum level for a planted aquarium
Aquarium plants benefit from 10 -15 mg/l (=ppm) of potassium. A level below 5 mg/l (=ppm) is not desirable and can lead to growth problems, yellowing of the leafs and deformations, Often lack of potassium is confused with lack of iron, also because potassium was very difficult to measure until now. If the level is too low, extra potassium will help the plants te recover soon and they will color deep green.