For last 4 years I use 90 gal. per day SpectraPure RODI. When my TDS reaches 0.01 then I'm replacing my Sediment, Carbon and DI resins. Did't replace RO membrane yet but I will this time. My question is really simple. I have always replace them with SpectraPure brand but they are quite expensive, for 4 of those cartridges I will pay around 140 $ ( best they have) Do you guys have suggestions or should I stick what works for me? I don't want to compromise health of my tank but just looking to save some money… Thanks for all advice.