04-11-2013, 09:03 PM
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Originally Posted by JDM
If you want maximum benefit, why can't you just pop a UV directly into the water? I am sure there are some units that don't have cases and pumps that you can submerge straight... might not be specifically for aquariums... issues with fish and UV exposure perhaps so put one in a PVC tube suspended vertically just off the bottom. The bulb will probably produce a bit of convection, keeps the flow low.
With the tank units you are dealing not only with high flow and low wattage but high turbidity that basically shades most of the water. The only exposure is that very first film of water against the lens unless you go inline after the filter and that is only good if the filter is doing a very good job of cleaning the particulates out... fine, fine filter media.
Because of fluid dynamics. The current in the tank is not enough on it's own to force the water through it (especially a twist design) in an efficient enough way. If you mean why can't you just put a UV bulb in the water, it's because it's harmful to look at - I imagine it would damage the eyes of the fish as well.
In tank units, like the green killing machine, work very well, without the water being prefiltered.