Potassium is one of the most important elements for plant growth and health; it is utilized in photosynthesis, maintaining ion (charge) balance, in the translocation of important organic and inorganic compounds (such as sugars and nutrients, respectively), and it is essential to many of the biochemical reactions taking place within plant tissues, as is evidenced by the relatively high percentage of plant tissue that potassium accounts for (second only to nitrogen). The affinity that a given species of plant shows for potassium may be partially dependant upon that species’ tendency to flower and form complex root systems (both of these correspond to greater potassium requirements than in bunch plants or those that rarely flower, per unit mass). Environmental factors such as light intensity and duration, and the presence of other nutrients in adequate concentrations, may also influence potassium requirements.

Because potassium is utilized in photosynthesis, a deficiency can lead to chlorosis, in which insufficient chlorophyll is produced and the leaves become pale; if not remedied, the plant may suffer extensive tissue decay (chlorophyll is utilized in the production of new tissue) and eventually perish. Chlorosis is likely to appear first in the older leaves of the plant, which tend to be on the periphery. In addition to potassium, magnesium, iron, and nitrogen are important to chlorophyll production. Maintaining a total iron concentration of 0.05 - 0.10 ppm, and magnesium concentration of ~5 ppm, is generally sufficient; nitrogen should primarily be present as nitrate at a concentration of less than 20 ppm. The required concentration of potassium may vary in different aquaria; it is recommended to begin by maintaining the concentration at approximately 15 ppm for the first week and adjusting the concentration by 1 - 2 ppm every two weeks as the appearance of the plants dictate; the recommended upper limit for potassium is approximately 30 ppm. The rate at which potassium is extracted from the water is largely dependant upon the rate of plant growth, therefore densely-planted systems with optimal chemical and environmental conditions are likely to require regular potassium supplementation.

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.