Expounding about the concept of Ultra Violet Sterilizer (UV), we should consider its strength and limitations so that we do not end up expecting something which the UV cannot perform.
First, UV is only effective as per its rated flow rate. Technically if UV unit has a capacity of 6 GPM (gallons per minute) then water flow should be maximum of 6 gpm so that the dose emitting from the lamp can effectively eliminate the microorganisms in water, however, if flow rate is higher than 6 gpm the dose will be lessen thus increasing the chances of microorganism to survive.
There are data that will show that as per bacteria spectrum, disease causing microorganisms can be eliminated at the dose ranging from 6000 to 10000 microwatts seconds per squared centimeter and beyond 10000, no disease causing microorganisms will survive, since the conservative lamp dose is at 30000,even 50% dose will still guarantee for the non survival of said microorganisms. However this concept should not be adapted since the NSF standard for UV dose is 42000 as per its rated flowrate.
Second, UV eliminates microorganisms as the water flows into the unit but after passing through, water is always vulnerable from bacteria.
Third, if turbidity is too high, then chances for microorganism to survive is greater since microorganisms can use the suspended solids as shield to protect them from ultra violet rays being emitted by the lamp.
Fourth, high level of hardness can cause quartz sleeve scaling thus lessening the dose of the lamp and increasing the survival rate of microorganisms.
In order for your UV to become effective, then you can consider this concept. Any clarification with these, just feel free to ask me here and I will be willing to entertain your concerns within the bounds of my capacity.