You get a slight build up of particulates when not using the RODI, using it regularly is good for that, and keeping the membrane in use is good too, you shouldn't let it sit forever.

I had actually been using my RO/DI directly to the float valves on my tanks and let them kick the solenoid on and off as required, but I found that I was exhausting RO membranes prematurely this way. At one point (you could even read about it here, there's a thread about it somewhere, I think from about a year ago) I went through 3 membranes in the space of a couple of months. So that's why I switched to filling up the reservoir, as needed, in one go (that's what was suggested to me anyhow). Maybe I should switch to a smaller reservoir - one that requires refilling slightly more often than the current 10 days it seems to offer me. Moving the float valve lower into the tank ought to do the trick.

I trigger my RODI once a day, I am still on my origital RO membranes, they are over 2 years old now, I haven't even flushed them out. I have gone through a few sets of the other filters & DI though.

My waste water production has probably increased, but I don't measure it so I don't know. Its probably time to replace my membranes.

At two years you might be getting close to needing to replace it. Then again maybe not. I think I got 3 years on my first membrane which is why I was so surprised at how finicky they can be after all.

Basically I wouldn't worry about replacing the RO membrane unless you get uncharacteristically high tds coming out. I.e., if you watch your tds then you'll know when it's time to replace it. I would get about 40-70 tds coming out which is still basically a tenfold reduction, so there was still function left, but still, obviously there's a problem if you get those kinds of numbers and not, say, 0 to 10.

I replace my prefilters approx. every 3 months.

Maybe when I come back from vacation I'll try a little experiment with a sprinkler solenoid valve, and just run the RO/DI every night for about an hour, and see what that does to the tds surge.

The only thing is I like running my reservoir empty between fills, that way I know I have water that's no more than "X" days old. I.e., if you run all time at near about the same level of water in the tank, then it becomes a pool of water that isn't completely refreshed periodically, and I can see that things like bacteria and whatnot could gain a possible foothold...

Sheesh - there is no end to the pros and cons of any idea, is there?? :neutral:

When you do a water change, you could use the reservoire water, then you know it is being 100% replaced.