UV-C clarifier for fresh and salt water aquarium up to 500l [123 US gal] 1.Reliably removes all kind of floating algae [green cloudy water] without using chemicals . 2.Reduces the multiplication of thread and other algae . 3.Reduces pathogens and cloudy water caused by bacteria. Powerful but very economical UV-C clarifier with multipurpose connection and for filters and pumps. The sera UV-C clarifier can be used in combination with a flow pump e.g. sera P 1200, or an external filter,e.g. sera fil bioactive 130 or 250. The performance of the pump should be the volume of the aquarium per hour .The UV-C clarifier can not be operated without a pump. Aquarium inhabitants and filter organism are not harmed by using the sera UV-C clarifier, which will give you permanently biologically healthy aquarium water this way. Variable hose connector; 15/20 mm