I have a UV on the end of one of my canister lines in my heavily planted 220g. I like the polished look of the water. As for algae, a UV only kills what passes in front of the light, therefore green water algae if the only algae it will kill. Some use products such as Purgen to give they water that ultra crisp look, UV's can do the same thing but remember with UV's you have to replace bulbs yearly. I don't see them as something needed for a small tank, except to clear green water, but on a large tank they really can be quite helpful.