I have had my tank for a year and have had a 9 watt UV on it since I started...I keep several soft corals and have tons of fanworms, pods and red coraline algea...I do not have any red or green algea at all...I have never had any serious fish diseases at all.,,except once when one of my chromis had a ailment...but I quarintined him and he is healthy now...I don't think its a necassry component but I do think that it makes husbandry a but more managable...