when to change RO/DI filters

[jacksonpt]

I've got a 5 stage rodi using a 1 micron, 5 micron, carbon, and di filters. Historically whenever my output line reads over 3tds I change all my filters/resin.

Tonight when changing the filters I got to thinking that might be a little inefficient. Is it necessary to change all filters every time? The 1 micron filter does get grungy, and the di resin does change color as it gets old... but is there a reson to change the other 2?

 

[SkiFletch]

What's the order you're using? The answer of course is tricky and really depends on your source water. As a general rule of thumb, a foam pre-filter should be replaced most often, and your two carbon blocks less-often. But if you have really clean source water, you might not even need to replace the foam that often. Personally, I run 10micron foam, 5micron carbon, and 0.6micron carbon pre-filters. My pipes must be wicked rusty caues the 10micron needs replacing every 3 months (gets nasty and orange fast). 5micron carbon 6 months, 0.6micron yearly just in case. RO membrane as-needed when flushing doesn't make it work again. For me that's around 5 years.

 

[cardiffgiant]

I try to change every 6 months, or whenever my water pressure drops. I notice that my water pressure drops if my sediment block is ready to be replaced.

 

[jacksonpt]

What's the order you're using?

5 micron foam > 1 micron foam > carbon > RO membrane > DI resin

Source is well water.

the 10micron needs replacing every 3 months (gets nasty and orange fast). 5micron carbon 6 months, 0.6micron yearly just in case.

Thanks, that's what I was looking for.

 

[der_wille_zur_macht]

DI: when TDS of output climbs above what you can tolerate
RO membrane: when TDS of output climbs above what you want to put in to your DI
Carbon: look up the manufacturer's rated lifetime (which will be in gallons processed), derate maybe 30%. Be sure to include waste water volume.
Sediment: Whenever it looks dirty. They're cheap.

I probably keep most of my elements in use longer than the average hobbyist. When this topic comes up on the open forums it's pretty ridiculous to see people suggesting carbon should be replaced at intervals that probably correspond to a tiny fraction of the rated lifetime, and they aren't able to provide a reason why. Basing your maintenance on a calendar only works if you know what your usage is over that timeframe.