A UV Can be a mans best friend. It must be installed properly,and have the right sized pump.... It deffanatley controls the parrasite from spreading. GOOD EXAMPLE...
I had a tank wipeout due to ich... one month later i added fish again and they were also infected..very frusterating....
since there were no fish in the tank and the parrasite were volnurable The UV did its job... So from my experiance...A UV Can Optimize water quality..not to mention got rid of alot of that bad algea