The Flowerhorn fish is able to thrive best in water of tropical temperatures, ranging from 76 to 84degrees Fahrenheit. The optimum temperature would be between 79 and 83 degrees Fahrenheit.It is advised that you maintain the optimum water temperature when keeping a Juvi or premature fry.PH Levels. Flowerhorn fish can survive in water with a neutral pH value of 6-8.he optimum temperature would be between 79 and 83 degrees Fahrenheit. It is advised that you maintain the optimum water temperature when keeping a Juvi or premature fry.PH Levels. Flowerhorn fish can survive in water with a neutral pH value of 6-8.