[Paul467]

Hi everyone,

Just found this forum on the net, i am from the UK, but i hope you won't hold it against me. i wonder if anyone could answer this question. When should you change the membrane on your RO unit. Mine says that it is ok for so many gallons, but as i only use it once a week, does anyone think that a time factor will come into play first. It would take me years before i changed it if i waited till till the amount of gallons they say passed through it. Surely, the membrane has a shelf life? Many thanks for any replies

[charlie]

Is it only an RO unit that you have , or is it an RO/DI? A TDS meter would be a handy thing to have to check this out. The ratings on the membranes are usually pretty true. I personally make between 75-100 gallons a week, and change out my membrane 1 time a year. Hope this helps you out.

[CSeaSee]

WELCOME TO REEFLAND!!!!!!
Some RO units have a "flush" system that extends the membrane life, as well. I guess another way would be to test your RO water for phosphates, nitrates, Etc.

[Paul467]

Thanks for your help guys. i have tested the water with a nitrate test kit and it is not zero as it should be. It is a Kent marine TFC unit, 1 micron pre filter 1st pod, a solid carbon block 2nd pod and then the membrane. I think that after reading your advice i should get a new set of filters, membrane and invest in a flush system.

Thanks for your help,

Paul

[jiggly75]

I have an RODI. I change my membrane when the TDS from the membrane goes above 5 tds. That way my DI lasts longer.

[kevinpo]

A TDS (total dissolved solids) meter is the best way to determine when a RO membrane or DI cartridge needs to be changed. If you are using a DI cartridge after the RO membrane then I advise changing the RO membrane at 5-8 ppm so the DI will last longer. If you just have the RO membrane 10ppm is the maximum I would go before changing the membrane. There is no shelf life but higher reject rates and lower supply pressures will extend the life of the RO membrane.
A hand held meter runs about $30 USD and an dual inline meter runs about $40 USD.

HTH,
Kevin

[Unresistible Blue]

When membranes go bad, you'll see that they begin to reject less of the tds in the feed water, or they produce less purified water ("permeate").

To start with, identify the brand and capacity of your membrnae (e.g., 75 gpd). Look up the factory rated rejection rate for the membrane. Use a tds meter to compare what you are getting to what you should be getting.

Its not really appropraite to ssay "change your membrane when the output gets to 8 ppm tds. For example, if you have feed water at 550 ppm tds, and you use a Filmtec 100 gpd membrane, a new membrane will produce 55 ppm tds water.