6mo is the recommended filter/external hoses/internal pump hoses replacement cycle.My Mastertronic and Alkatronic have been running for 2 months now and I haven't changed the filters so far.
I'd be definitely interested in finding a reasonably priced alternative. Please post your findings.
I checked the user's guide and I couldn't find how often they should be changed.
I guess I would change them if I see stuff growing in it or if I notice a large volume change during the pump calibration procedure.
I looked for similar filters some time ago since I perform continuous water changes with DOS pumps. I ordered some fuel filters following a post I found here but they came with a metallic cap and won't work (the picture didn't show the metalic part).