I also have the Aqua UV 57 watt on my 170. ( highly recommend )
To control ICK flow is key. For around a 200 total water volumn, you will need to treat the water frequently enough to keep up with the regrowth, and have a strong enough dosage. You will need to get the flow between 600 and 1000 GPH going thru the U.V. to control ick.