UV sterilizer

The best way to control disease is to quarantine. There is a lot of debate about UV units, so you'll probably get varying opinions. There is the possibility that you'll be killing off more good stuff (like zooplankton) than bad. On the other hand, a properly sized and run UV unit can eliminate some diseases.

To me, it's just another contraption to have to maintain, expensive bulbs to replace, and more heat going into the tank.

If you get one, I found the Aqua UV unit to be very well made.

I'm in the 'anti-UV' contingent. While I can see using them in a quarantine tank, or possibly on a FO tank, using one in a reef kills off a lot of beneficial organisms. A chum of mine added one to his tank, and within about 2 weeks his nitrates sky rocketed. So he got a denitritifier, which was costly and a pain. After a month of so of fighting, he took the UV off, and within a month his nitrates were back to normal levels.

The other problem--UV will only remove the parasites while they are free-swimming. It's unlikely to remove all of the them, so IMO, you end up with fish that have a sub-clinical infection, and any stress event can induce a full blown outbreak.

I'd prefer a good quarantine any day.