I have found that it is really obvious when the membrane is pooping out... production rate goes down drastically. TDS rises only a bit (still in a decent range) when I run out of day to refill the barrel. It's not subtle.

Ah HAH! Context DOES matter!

Yes, there are volume totalizers - The FM-2 I mentioned earlier is one, but it goes on the input of the system.

As far as "if the output falls", that would be a subjective thing to me. "Hmm... I used to get my gallon in about 20 minutes. Now it's more like a half hour."

It's more like "it usually fills the barrel from the morning watering by 2 PM, now it isn't done at 5 PM in time for the effluent dump through the sprinklers". Not subtle...

Yeah - I used to have that perspective, but my collection and use of RO is a LOT smaller now.

This makes perfect sense. I'll probably just time it every now and then when filling up the smaller container I use for my MistKing. Good to know your TDS doesn't drastically change. I'll watch both.

The TDS may drift upward. If it’s 3 now, I’d think about a new membrane when it gets above 10.

About the ratio that I work with... a new membrane gives me about 10, about the time that the production goes down drastically, the TDS may be up to 20 or 25. Not a rush though.. it is still, at its worst, a 90% or better improvement over the input, and by that time it's so slow that it gets replaced anyway.

The primary issue I have with TDS meters is that you don't know if the "10" ppm you get with a new membrane is real. It could be anywhere from 1 to 20 or so. Not that that's a big deal, but it can be when using it to control fertilizer concentration.

Read this is you don't mind being "Nyed".

Me, I'd already read it. And was so Nye'd my head swum. :biggrin:

Now for a question... why does Roberta's TDS start out at 10 and mine starts out at 5? (and I've been using same cartridges for awhile). Plus I'm pretty sure Roberta has better water than I do.

First, at those low levels I doubt that my meter is particularly accurate. I look for changes more than an absolute value. The other may be the specific membrane design (my unit is pretty efficient with water use at least when the membrane is functioning well, but may let a little more though) That's actually another clue when the membrane is on the way out... not only is the production slower, but seems to produce more effluent for the amount of good water. I do beat the poo out of the system, especially in summer.