[Reef_Geek]

I don't think the UV has any impact on non-living material (e.g. dissolved proteins).

UV sterilizers work by irradiating the DNA of micro organisms in the water that passes through the chamber, making the DNA non-functional in cell replication. It doesn't kill the organism instantaneously, but instead, renders it useless in reproduction to interrupt the life cycle.

UV effectiveness depends on the wattage and contact time for irradiation. Additionally, if much of the water is able to bypass the UV flow circuit, a significant proportion of competent microbial population remain in the system to replicate.