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UV's sterilize the water pretty well if the bulb is still good and it is an appropriate size. Sometimes they can be bad if they are over spec or on too long and the will take out too many beneficial organisms as well as the bad ones.
UV filters are good if used properly. You just have to install them in the right place, have the correct amount of water flow through them and make sure you change the bulbs every 9-12 months. There is no need to have a timer on it.
It should be on the return side. The water that goes through the UV filter should be as clean as possible. Dirty water will inhibit the UV light from passing through. If you know the Wattage of the UV filter and the size of your tank you can calculate the water flow you need for it to work properly.
That UV filter is a little small for that tank. The flow rate throught the filter should be ~4gpm which is hard to do. Usually for a 75g tank a 25 watt or higher UV filter is used. But since it is not really needed for keeping a ceph you can have a high flow rate through it, but if you double the flow rate than it cuts how effective the filter is by half.
There have been some issues with UV if you want to breed, there seems to be some mutation occurring in mollusc and crustacean larvae even if they don't pass through the UV (deformed shell, foot, damaged internal organs, increased moult death syndrome in the crustys) the problems all vanished when the UV was removed. So I'm hesitant about it even if you're not planning on breeding. course I could just be prejudiced!