Are the fx5 hoses 1" i.d. or o.d.? I have hydor eth heaters for 5/8" hoses on my fluval 405s and have been tossing around the idea of replacing one 405 with a fx5. If the hose is 1" o.d. It will be 3/4" i.d. which is only 17% larger than the 5/8" needed for the heater, if 1" I.d. there would be a 37% difference which will probably put to much pressure on the motor. Any thought will be greatly appreciated.