[karimwassef]

UV will kill organisms in the water column.

Most bacteria and pods and benthic = not in the water column. They live in rocks/sand/etc...

Dinos leave the hard surfaces and live in the water column when it's dark. They become particularly susceptible to death by UV if the flow is slow enough.

I run a multi-day dark period with UV and heavy wet skimming and carbon. The dark made them take to the water column, the UV killed them, the wet skimming removed their dead tissue and the carbon removed any toxins.

The survivors were eaten by the pods who came out in the dark to feed.