Membrane life

[Duce]

OK I have my RO/DI units for several years already. My question is when to change the membrane. My TDS is measuring 0, 0 Nitrate and 0 Phosphate for the water coming out does that mean my membrane is still OK?

[alex9421]

OK I have my RO/DI units for several years already. My question is when to change the membrane. My TDS is measuring 0, 0 Nitrate and 0 Phosphate for the water coming out does that mean my membrane is still OK?

Are you measuring the TDS of just the RO water or the RO/DI final product. To know if your membrane is still functioning properly you should measure the TDS of your incoming tap water. Lets say 100 ppm for example. Then measure the TDS of the water after the RO membrane (no DI). Now depending on your membrane rejection rate for example mine is 95%, if your RO membrane is functioning properly the TDS should be around 5ppm. Anything significantly higher and your membrane is not functioning properly.

[Duce]

I am measuring the output of my RO/DI unit - final product.
I have measured the TDS of my tap water and it is significantly higher...it is over 100.
Does measuring the RO vs RO/DI makes a difference in my scenario?

[H20_Science]

Alex is correct, Measuring the RO DI is important to know wether or not your DI is functioning but it does not help you with the RO as the DI will cloak any performance issues from the RO for a while but you will burn out your DI much quicker. In order to know the status of the membrane you need to measure the water before the DI and as suggested by Alex make sure the results are around 5% of the incoming.


Bryan Crenshaw