The invention provides a formula of a special water purifying agent for aquaculture. The formula is prepared from the following components by weight percent: 5 to 30 percent of isopropylamine, 5 to 20percent of water, 8 to 25 percent of L-carnitine, 10 to 20 percent of epichlorohydrin, 1 to 10 percent of absolute ethyl alcohol, 3 to 20 percent of OP-10, 0.5 to 3 percent of elemental iodine, and 1to 12 percent of phosphoric acid. The product is a nontoxic and pollution-free environment-friendly product, can effectively inhibit the growth of viruses, bacteria, fungi, harmful algae and the like, has the characteristics of high efficiency, durability, high penetrating capacity, small application dosage and the like, and can be widely used for purifying culture water and preventing diseases of aquaculture animals. The product is the water purifying agent and is specially used for sterilizing and purifying the culture water; and meanwhile, the water purifying agent is also used for preventing and treating skin ulcer syndrome, stomach ulcer disease and piebald syndrome of sea cucumbers, and white spot syndrome, early death syndrome, acute hepatopancreas necrosis and the like of shrimps.