josh a UV sterilizer didn't stop your fish from dieing , that was due to poor water quality most likely!.man you need one asap! lol i had problems with fish dying and the water in my tank looking like shit until i got one haven't had 1 fish die now that i have one and the water looks awesome, they help ya tank heaps you can get one for about 100 bucks , they are a must you hook them up to the return pump