You can run a UV
off your canister but beware of the recommended flow rate as I think Guage had mentioned earlier. This should be on the low side of the MFG's ratings in GPH
Inches of head pressure, hmmm, never heard that before - usually its feet of head pressure. But Inches works as well just wanted you to becareful of units of measurement. Anyway this is a method of relating backpressure on a pump, either due to the work the pump has to do to lift the water or due to something resisting the flow of water like a canister filter.
Pumps are rated in max head pressure - this means that if you use the pump to pump water straight up (i.e. against gravity) it will pump it to that hieght before stopping. For example if a pump has 1000 GPH
rating at 0' feet head pressure and 500 GPH
at 10' and it's max is at 20 feet then if you pump water up an 18 foot pipe the pump will produce some small amount of water at the upper end of the pipe. If you use a 21 foot pipe the pump will stop running.