... and the math says that parasite kill is a function of both light intensity and exposure time. Obviously you can increase the light intensity by going with a higher wattage unit ... at a higher initial and ongoing operating cost ... but also with increased water heating side effects, which can potentially create a significant tank overheating problem. The other side of the equation is to extend exposure time, which translates into a UV
unit with a bigger 'body' and/or a slower flow rate. This is the main reason that I chose to go with a Pentair unit, which has several times as much water volume thus several times as much exposure time as most 'inline' UV
units in the same wattage range.