RODI TDS after changing filters

[cdc84]

I am going through DI resin faster than I thought I would. The TDS after the membrane was about 15 so I bought a new Filmtec 75gpd membrane and replaced my sediment, GAC and carbon block as its been about a year since I changed those. After changing them flushing a few gallons through the pre filters then the RO membrane this is the results I got.

TDS into sediment: 385
TDS after pre-filters: 375
TDS after RO Membrane: 16 With the rejection rate calculating to 95.73% About the same as the Amazon RO membrane that I replaced.
TDS after DI: 0

From what I understand the pre filters hardly remove any TDS and instead catch the bigger particles and remove chlorine. Does the RO membrane take time to really start working I was expecting the TDS to be less than 10? I am thinking I should have purchased a Spectrapure 99% membrane but it costs twice as much.

 

[joseserrano]

Your tds should be under 10 after membrane. You may need to use catalytic carbon to lengthen the life of your filters

 

[Discotu]

Are you flushing the ro membrane before each use? If not all that TDS creep is going straight into your di resin. Also what is your water pressure? Finally make sure youre using the correct flow restrictor for your ro membrane.

 

[drexel]

My limit is 4 after the membrane, then I replace the membrane. Something tells me that this system isn't set up correctly. I also think you're gonna need a 5 or 6 stage system minimum to make decent water. You need a sediment > two carbon blocks > membrane (Geek Pure from Amazon are great and just as good as Dow for much less) > at least two DI resins (cation > anion or two mixed beds). PSI needs to be above 40, but ideally it should be around 60-70psi to be effective. If you pressure isn't high enough, you'll just burn through everything and the membrane becomes useless. So a booster pump may be necessary and there are a few options that will help and can provide auto flushing.

 

[drexel]

https://aquaticlife.com/collections...or-50-100-gpd-reverse-osmosis-ro-di-systems-1

 

[Jimbo327]

Also, get a water report from your water company. It'll tell you a few things.

I usually look for how bad the source water is, and what is it high in? If you have very high source water...then your RO can only reject 9X%, so it's a function of your source water TDS.

I know my water has a lot of silicates, so I actually split my DI resins from mixed bed to 2 chamber...one for anion and one for cation. This helps me change out only the ions that gets depleted.

https://www.bulkreefsupply.com/anion-single-bed-color-changing-bulk-deionization-resin-brs.html

BRS shows you which cation or anion is targeted. In my case, silicate is attracted to anion, so I sized up on the anion DI chamber.

As far as RO, make sure your flow restrictor is sized correctly to your RO membrane.