UV Sterilizer wattage

[Ice]

How much wattage in UV sterilizers do I determine I need for up to a 40 gallon tank ? I know someone told me it's a good idea to have one to prevent green water and epidemics (ie : ich, etc ...) What's a decent brand to get ? What do I need to look for when shopping for one ? How is it set-up in the tank ? Is it usually set up in the sump ? Are they any benefits to the corals such as xenias, polyps, or mushrooms ?

[Fishfirst]

the best way to prevent epidemics is a quarentine tank... they are actually slightly detrimental to corals because they kill micro organisms the corals feed on... I prefer the turbo twist models because they have more contact time. Set it up anywhere you want it.

[Reefneck]

I do not advise ever using a UV on a reef tank for any reason! Kills too many of the good organisms.

[TheOldSalt]

On the other hand, giving a few amphipods a suntan sure beats the heck out of having an ich epidemic wipe out all your fish. I don't suppose that the hobbyists of the world will ever agree upon the use of UV, but I would suggest about 25 watts.
UV wipes out the tiniest stuff on the very bottom of the food chain, such as the stuff upon which your more important microcritters feed, and this can yield bad results if you're trying to build a dynamic ecosystem. If you aren't trying to build such a system, and simply want your macrocritters to live disease-free, then UV is a simple way to go, although you'll need to perform more feeding and maintenance to replace what you lose.
Benefits to the corals? Well, as the other guys already said, UV will cost them some food, so depending on your coral species, that can possibly be a big problem. On the other hand, UV produces ozone as a side effect, which will raise your ORP and nitrify your ammonia and nitrite. It also cuts down on the organisms which cause numerous coral diseases as well as fish diseases, and it can even zap the eggs of planarians and other pests. On yet another hand, certain compounds/additives can be oxidized by it or the ozone, which can be wasteful.

So, the use of UV has a lot of pros and cons to consider. Either is fine, in my own opinion, so long as you are aware of the effects your choice will have and you work to compensate.

FishFirst already beat me to it, but quarantine is the real key. -->PROPER<-- quarantine will keep the diseases out of your tank in the first place, thereby negating any need for UV anyway. As for algae control, UV only treats the symptom, not the cause, so address the causes and you won't have any algae in the first place.