My advice is to check the required "dwell time" for your UV to function properly. All reputable UV dealers list acceptable dwell times for their sterilizers. In a strange sense, slower flow is better for UV because it allows them to sterilize more efficiently. Find the UV unit's rated dwell time, compare that to your pump's rated flow rate, and adjust for other in-line flow obstacles (filtration, heaters, etc.). It never hurts to use too much UV, IMHO, so buy a unit that may be over-rated for what you're doing.