When to change RO/DI filters?

[d_icemand]

I have a 4 stage Spectrapure RO/DI unit that I changed all filters, including the membrane, last year about this time.

I have a TDS meter starting to read 18 ppm. I am used to it reading 0. At what point should I change filters and which ones? I thought I read membranes are good for years. Should I change the other 3 which are carbon, Sediment, Mixed bed DI????

dave

 

[GlassReef]

If you have a 75gpd FilmTec membrane you should be getting approx. 96-98% rejection rate. So if your raw water is 250 TDS, for example, your water exiting the membrane should be 24 TDS or better. If it's higher change your membrane. I usually change my carbon and sediment filters every 6 to 9 months. If your getting 24 or less TDS from your membrane and your DI doesn't bring it down to zero, you probably need to get new DI resin.

 

[Henry Bowman]

I change all my prefilters every 8 months or when effluent TDS starts to creep up above 5 ppm. I change DI resin when it is exhausted.

After changing the prefilters and making sure the DI is good, my output goes back down to "0"

 

[d_icemand]

dumb question but how do you know when DI is exhausted?

sorry, but I am still new to some things.

 

[ERICinFL]

<a href=showthread.php?s=&postid=15539835#post15539835 target=_blank>Originally posted</a> by d_icemand
dumb question but how do you know when DI is exhausted?

sorry, but I am still new to some things.

If you have color change resin, well... the color will change. Mine starts out blue and turns tan/brown when it needs to be replaced. The resin at the bottom generally changes first and when it's half way up, I'll scoop out the good and dump the bad. I'll put the good back in, then top off with new. Seems to work for me.

 

[d_icemand]

I guess I will change the Carbon block, Sediment filter, and Mixed DI cartridge.

Usually my water reading going in is around 250 and my output is zero.

 

[SpectraPure]

fwiw-
more details specific to your system are availible in the system manual found on our website:

http://www.spectrapure.com/manuals/PRINTER_FRIENDLY/CSPDI_MANUAL.pdf

Also, when you mention TDS, are you observing the TDS of the product water post membrane, or fro the output of the DI section? What is your tap water TDS?

hope to help
bruce