because of the life cycle of ich, the odds of ridding the tank of ich with a UV sterilizer are extremely slim. the only way you could do this is if the entire tank was under a UV light for a full life cycle and that, Depending on the water temperature, can take from 4 days to several weeks., and we know we can't do that.
no matter how fast or slow water travels through the unit, it's not going to kill all of them.