[fencer]

Mark is essentially right there are only a few manufacturers no doubt that DOW relabels some of there RO filters to other companies. If I bought an RO filter made in say Afganistan I might wonder about the quality. I was told most RO membranes have a lifetime of at least 2 years or more depending on the duty. What will shorten the lifetime is excessive differential pressure cause by plugging or chemical decomposition(which is why you have all that prefilter), or by the booster pump. I imagine the only way you can tell is by TDS monitoring or if algae starts blooming in you tanks for no reason. You can buy pharmecutical grade RO membranes for $$$$