This is not based on my experience (I don't own one now, but have used them extensively in mollusk larvae aquaculture in the past), but on critical thinking and on published research (may be able to provide references later).
LOW FLOW (thru the light emitting unit) is needed. NOT high flow. Extended contact time of passing volume of water through the light is what is needed. If flow is too fast, no matter the turnover rate through the unit, the pathogens will not be efficiently killed and residuals will always be there to reinfect, thus maintaining undesirable populations.