cartridges should be changed out around 6 months of use if not too heavy. membranes can last up to 2 years under moderate use and depending how bad your source water is. Also, should be back flushing your RODI unit after use. I'd change everything out after drying and giving a good cleaning. Funny thing is I had a bloom when I wasn't using mine too often. Probably because even water in a filter can become stagnant. Also, make sure to run some water through the new filters to get any residue out.