BRIGHTY K is a liquid fertilizer for supplying potassium to a planted aquarium. When potassium is insufficient, the photosynthesis activity and growth of aquatic plants are affected, and this can cause yellowing and bleaching of leaves as well as lower resistance to algae. Daily application of BRIGHTY K to the aquarium eliminates these problems caused by potassium deficiency and promotes growth of aquatic plants. BRIGHTY K also has an effect of enhancing the buffering capacity of water and prevents a decline in the pH of aquarium water. BRIGHTY K is strongly alkaline. The pH of aquarium water may rise temporarily immediately after this product is applied, but it will eventually return to the original level.