You can use a UV as it helps in the killing of unwanted bateria.
You can also use a 3 watt it should be fine 9 watt would be over kill but that is what I usually prefer.
UV sterilizers can be plumbed in two ways, either "hard plumbed" or "soft plumbed." Hard plumbing is a permanent installation involving adhesives and PVC piping, while soft plumbing is semi-permanent involving flexible tubing and clamps. Knowing the plumbing style of the fittings on a UV sterilizer helps you select a compatible pump, as well as other plumbing supplies. Fittings for UV sterilizers come in three styles:
Barbed/Insert fittings - Commonly soft plumbed and the easiest to plumb since the appropriate-sized flexible vinyl tubing is simply fitted onto it and secured with clamps. Most hang-on sterilizers will have barbed fittings.
NPT (National Pipe Threading) fittings - Sterilizers that incorporate NPT fittings are either MPT (male pipe thread) or FPT (female pipe thread). Depending on your current system, NPT fittings can be hard or soft plumbed. However, the use of "NPT x Insert Adapters" can make plumbing easier since they convert NPT fittings to barbed or insert fittings.
Slip fittings - Usually hard plumbed but a combination of both plumbing methods can be applied using reducing bushings. A "Slip x FPT Reducing Bushing" converts a slip fitting to a NPT fitting which is then converted to a barbed or insert fitting for easy installation
