I would like to purchase some Inflow/Outflow pipes for my ZooMed 501 filter. I'm a little confused on what size to order, some say 9mm some say 10mm or even 11mm. I measured the tubing with calipers and came up with O.D. Of .45 which would suggest 11mm pipes. Anyone out there using pipes on a Zoomed? What size did you go with?