I use uv sterlizers and think they are a good tool. They are not a substutute for good water quality nor a quarantine protocol nor effective treatment of disease.
A uv sterlilizer could not kill a pod unless one chose to live in there. It does kill waterborne bacteria and algae(including phytoplankton) pretty effectively.
It stops green water from excessive phyto and makes glass cleaning needs less frequent.If you keep animals that require more p[hyto than the sterlizer leaves in the water it can be easily supplemented.
A sterilizer's lethality depends upon the amount of radiation an organism receives relative to it's size. A higher wattage delivers more rads and so does longer exposure(slower flow or dwell time). Bacteria and algae are relatively small and smaller sterizer's are more effective against them.The bacteria effected are waterborne without much if any effect on the denitrifying bacteria in/on your substrate.
As for Ich, there are two kinds;cryptocaryon irritans,a protozoan parasite which is too large to be killed by the uv unless the strilizer is oversized and/or water passes through it very slowly. However,
the other ich,amyloodinium(sometimes called velvet) is a dinoflagellate algae. Amyloodinium is almost always fatal and destroys gill tissue very quickly. Otherwise healthy fish can sometimes shake off cryptocaryon. In a weakened state from cryptocaryon they do ,however, often fall to amyloodinium or secondary bacterial infection .
For clarity, A uv sterlizer is not a substittue for quarantine or treatment. It is a good supplemental piece of equipment and can help the health of your tank.
