$49 CRYSTAL CLEAR - Turns CLOUDY and GREEN water crystal clear in 3-7 days. The larger the fish tank, the longer it takes. Reduce the number of water changes in the fish tank. DOUBLE FILTRATION - First stage Biochemical Sponge Filter. Second stage 254nm wavelength U-V Light treatment. SEPARATE SWITCHES - Control the water pump and fish tank light separately. When you only want to use the aquarium filter function, you can turn off the fish tank U-V light separately. SMELLS FRESH - Once the fish tank is full of green will be accompanied by the smell. This green killing machine can reduce the unpleasant smell in the fish tank. EASY TO CHECK LIGHT UP - You can easily check that the light is on from the outside of the machine, don't need to take the machine apart to see it..