Best bang for your buck. You can add a TDS to this unit, this way you know how good your filters are. All that realy matters is a "0" TDS(Total disolved solids). Majority of filters last 6-12 months, depending on the amount and quantity of water changes. Also depends on your water quality. You can get a hand held TDS meter and test your water. Our water fluxs from 100-150 TDS, with an ro/di it is 0. As for filter's, spongue filters are pretty good.
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