You can run them how ever you want. Get only the sterilizers and not the clarifiers. I would not go lower than 25Watts. Make sure to get the ones with the sliding cleaner rails on the inside. If the quartz tube gets dirty, and it will every couple of days, the effectiveness goes way down. They will make your water clear. They will also reduce the number of free swimming parasites, not eliminate them. They will kill most of the algae and pods that go through the unit.