Where is the best place to put a UV Sterilizer?

I bought a new UV sterilizer and I'm not sure where the best place is to put it in my tank. My fish have Ich right now (stage 1-- white spots on body) and I'm treating them with heat, salt and hopefully the sterilizer can kill a lot of those parasites.

Right now, I've put it between two filters (an AC 110 and an Eheim 2217). I would think that the more water passes by the sterilizer, the better chance it has of catching any pathogens.

What do you think? Where is the best and most effective place to put a UV sterilizer?

I wish I could attach it to an outlet, but my UV sterilizer is an in the tank one. It's a 9watt sterilizer on a 100 gallon tank. Flow rate is 50 gph. Here's a picture of it: