i use uv on freshwater and its a sure bet that your water is on the cleaner pure side that your tap.... ive heard every saltwater tank should utilize uv
I use it in freshwater and it's worked wonders... seems to keep the tank ticking over and the water clearer... it runs 24/7 and is just in line with one of my canister filters.
If any harmful bugs or bacteria get into the water UV can help in killing them and stops the spread of any diseases through the water....