How practical would it be to make a DIY UV light? I've never seen a commercial one, but it seems like it's a rather simple device.
The quartz sleeves and light tubes can be purchased from various pond equipment suppliers. I suppose the light tubes might work with regular flourescent tube ballasts. Prices seem to suggest that one can be made for around half the cost of a commercially made one.
Perhaps something like this can be added off the side of a skippy filter or other gravity part of the plumbing (don't even need the quartz tube in this case):
A pressurized version of the same thing would just add the quartz tube (and a way to seal it) to protect the bulb from the water.
This doesn't sound very difficult to me, but I'm not finding anything on the web to make one.