How often should I replace RO/DI filters in a reef tank?

Replace sediment and carbon filters every six months for most reef systems. Change DI resin whenever post DI TDS rises above one to two ppm. Test RO membrane performance monthly by comparing tap water TDS with RO only TDS. Replace the membrane when rejection falls below about ninety six percent. Check pressure regularly because low pressure reduces membrane efficiency and burns through DI resin faster. Flush the membrane after changing prefilters and inspect canisters for trapped debris. Keep spare prefilters and DI resin so you can swap immediately when readings increase. If your source water quality shifts by season, shorten replacement intervals and test more often. Consistent filter maintenance helps prevent nuisance algae, reduces coral stress, improves stability during water changes, and keeps long term costs lower by avoiding emergency livestock problems.