Brightwell Aquatics Florin-K is a high-purity potassium supplement, and is free of chloride (while chloride is a vital element to plants, it is required in a very small concentration, provided in Brightwell Aquatics FlorinMulti). Because the potassium requirement of aquatic plants is high relative to that of other nutrients, Florin-K is very strong (50,000 ppm), making it an effective and economical potassium source.