RO filter replacement schedule?
 

Just got a 5 stage RO system from FirstRay with some flush rate reducer, to replace a DI set-up. Filter replacement schedule is:
Sediment filter 6 months/3000 gal
Carbon: 12 months/6000 gal
Membrane 18 months/9000 gal

I assume this is like oil-changes on a car: which ever comes first.

I am a rather low user, say 3-5 gals/day, so that is 1000-1500 gal per year, and don't want to put more in the landfill than necessary.

Are you sticking to the "official" replacement schedule or do you extend it? I am most inclined to stick with the official membrane schedule, but wonder whether sediment and carbon can be prolonged a bit more. Local water TDS is on average around 350.

First of all, my recommendation on the membrane replacement is 24 months/12,000 gallons. The fact that you have opted for a greater reduction in flush water may affect that, so I suggest that you rely on testing to confirm that need.

Those are industry standards, so I stick with them from a recommendation standpoint, but unlike motor oil, which builds up acids that can degrade it just sitting there, there is nothing that will require you to replace the components more frequently than the volumes called-for.

Not sure what Ray's unit comes with, but an inline tds monitor is an easy and inexpensive way to know precisely what condition your membrane is in at any time. Units are available with multiple channels, to allow monitoring of the feed water, the water exiting the membrane before it enters the deionizer chamber, and the finished product water at the slide of a switch. An inline pressure gauge located between the final prefilter stage and the membrane to monitor pressure rise over time is a more accurate guide to their replacement schedule. The life of these components is naturally highly dependent upon the water entering the unit. To my mind the prefilters are cheap enough to replace routinely, at least for home use, but membranes are a different matter. For my current situation using relatively large amounts of ro/di in my aquarium maintenance business, I want the maximum useful life for all components.

I follow Ray's recommended schedule, but also regularly test with a TDS meter. Brand new, I was getting readings of 8ppm. After more than 1.5 years of use (I make about 15-20 gallons a week), the TDS has started to slightly rise and is now around 25ppm. So I will probably change the membrane soon.