[christyf5]

It also depends on how often you use your RODI. I only used mine for probably about 10gallons per week with a 15 gal water change every 2-4 weeks for the first couple of years that I had mine. This past year or so I've upped it to about 20 gallons a week as I've been doing weekly waterchanges without a sandbed.

Personally I'd just replace them every 6-9 months or so, even though the water is pretty clear here and the TDS is low, those 5 and 1 micron filters can get pretty clogged. As well as the chlorine in the summer that might make it past the carbon filter if its run down and ruin your RO filter.

I also managed to get in on a group buy of filters. Buying them this way saves a ton of money (esp on shipping where Aquasafe really gets ya). I got 6 changes of filters and 4 changes of DI resin for just over $100 which makes it about $17 per filter change (with the DI ones more sporadic as theres only 4 changes of that). I priced out the filters from various stores and calculated that it would cost me about $30 for the sediment and carbon filters per change. The DI filter was about $35 on its own (not the refillable resin type though). Although you might be able to get these cheaper at a hardware store or water purification store.