Im using a 57w on my discus tank with a rena xp4, 350gph. Been happy with my purchase ever since.
Most GOOD UV sterilizers that i have seen are inline, in which case you would have to change your filtration. I would recommend doing that any way if you are only running hang on filtration. With a 75gal tank consider what load you have and how much you want to stock to determine best filtration. Sump and canister filtration are two of the best ways to go. I use to run two canisters on my 75gal tall. That was until i figured out how to maintain my tanks with proper WC and care.
Also what substrate do you have? Is it a fert? If so, if you were aggressive adding the water back in and stirred up the sediment, i would not be suprised if it took a couple of days to clear up. Chemicals should never be your first choice.
Check your filter pads in your peguins, are they dirty? clogged? saturated with sediment? That happens to my other filters and after a rinse they clean up the tank nicely.