Seachem Flourish Potassium 500ml (17 fl.oz) contains 40,000 mg-L of potassium suitable for the natural freshwater aquarium. Potassium is one of the vital elements essential to sustain a vigorous level of plant growth. Potassium can be depleted in a rapidly growing aquarium or when a source water has a low mineral content. In these cases potassium can become the limiting factor to growth. Use FLourish Potassium to prevent potassium depletion and to maintain the highest level of growth. A 100 ml bottle treats 80L (20 gallons) for 4-6 months