are you sure its 300gpd unit as picture is not good quality . i would say its 200gpd with separate di vesel . even so your filters will last some time . i use ro-man 200 gpd unit with di set up more or less the same as your picture . the 3 bottom filters i change around every 5 months the membranes i have not changed and had my unit some time . i was told in a aqua shop that if you back flush regular your membranes will last a few years . i cant say on this but my units still working well and only changed pre-filters once .