My RO membrane is 3 years old

[b4tn]

I have replaced the other media 3 times now. I’m still getting 0 TDS when does it need replaced?

 

[Brad Miller]

Most that I know of or use will turn a tan color, indicating a need for change, but people do a yearly of all cartridges once a year that don't want to risk anything.

 

[pecan2phat]

I've had membranes last 5+ years, it all depends on how clean your water source is.
Best gauge is a TDS meter monitor after the membrane, before the DI resin. When the TDS starts to creep up more then the specs (ei: 97% rejection rate) then it's time but you would also need to know what the water source TDS is also.

 

[Brad Miller]

Pecans right, also depends on how much water you use too.

 

[Water Dog]

If it’s running to the membrane’s rejection rate specifications... Dow Filmtec 75gpd is 98% or Spectrapure 90 is 99% as determined by the TDS of your tap vs the TDS after the RO membrane, then there’s no need to replace it.

 

[b4tn]

I have the BRS 4 stage 75gpd with TDS meter. I’m asking because my DI is used up and am ordering replacement DI along with the other cartridges. My TDS is still 0 even with used up DI. But I read 5 TDI in and 0 out. I make about 1 gallon every 25 min.can I find rejection rate from any of this?

 

[redfishbluefish]

You certainly can determine the rejection rate, but it really isn't necessary. What you need to do is simply keep an eye on pre DI TDS. If should remain steady (after it's been running for five or so minutes.) If and when you start to see that it doesn't remain at that low number, and is creeping up, it's time for a new membrane. FYI, my membrane is over ten years old.

Now, to determine rejection rate you need to know your raw water TDS (coming out of the tap) and the TDS pre-DI (before going through the DI resin). To calculate rejection, do this simply math:

((Raw TDS - Pre DI TDS)/Raw TDS) x 100

An example with RAW at 150 and Pre DI at 2:

(150-2)/150 x 100 = percent rejection

148/150 x 100 = percent rejection

98.7 = precent rejection

 

[billwill]

I change mine out now every two years. My experience after not changing for over 5 years was algae issues regardless of what tds meter showed. There’s more to water than just what we measure, but that’s just my opinion