Tds before RO

[lmfbs]

I'm setting up an old but basically unused RODI. The RO membrane is new.

Tds tap: 68
Tds after sediment, 2 stages of carbon: 52
Tds after RO: 7

I havent connected the Di yet because I think my tds isn't getting low enough before the RO. What's yours after your first stages before RO? Should I replace my first 3 filters?

 

[Townes_Van_Camp]

You arre over thinking this. My city water in is 210-240. My spectrapure 90 gal/day system for drinking water gets me to 11 TDS. I have an Identical system for my tanks, but have added the Di stage. It gets me to 0 TDS. Granted, I do nano's 25 gal and 15 gal so I don't care about yield as much as someone who is making tons of water. If you want to geek out, geek out on making sure you have sufficient pressure (60-70 psi at the supply).

 

[gbroadbridge]

I'm setting up an old but basically unused RODI. The RO membrane is new.

Tds tap: 68
Tds after sediment, 2 stages of carbon: 52
Tds after RO: 7

I havent connected the Di yet because I think my tds isn't getting low enough before the RO. What's yours after your first stages before RO? Should I replace my first 3 filters?

TDS out of the membrane should be lower than that.

What does the pressure gauge going into the membrane say?
Does the flow restrictor match the membrane rating?

 

[Townes_Van_Camp]

TDS out of the membrane should be lower than that.

What does the pressure gauge going into the membrane say?
Does the flow restrictor match the membrane rating?

My rejection rate is fine. Hers lacks a little. But not so much she should worry. Unless, she uses a lot of rodi. In which case a tune up is needed. I essentially say that.

 

[Dbichler]

Are you sure your membrane is seated correctly. With that low of tds there really shouldn’t be much of any tds after ro.

 

[Troylee]

Vegas water coming in is 570 tds… after my membrane it’s coming out 5-7 with the help of a booster pump at 80psi… without the booster and running on city pressure of 42psi my tds was 12-15 after the membrane and killing my di resin bed.

 

[chipmunkofdoom2]

Your system is operating as designed. The RO membrane is where you'll see 90%+ of the filtration happen in an reverse osmosis system. The prefilters don't do much besides protect the RO membrane from failing prematurely.

The one thing that might need some attention is your rejection rate. The RO membrane should be able to remove 90%+ of solids in the water. So if the water going into the membrane is 52 ppm TDS, the water coming out should be 5 ppm TDS or lower. Check the water pressure going to the unit, and check the pressure between the prefilters and the membrane to make sure they're not clogged.

Also check the flow restrictor. Many manufacturers put comically undersized restrictors on RO units to make them more "efficient." The actual result is that the membrane is choked for brine and can't filter water properly. Most membranes are designed for a 4:1 brine to permeate (waste to product) ratio.

 

[lmfbs]

Are you sure your membrane is seated correctly. With that low of tds there really shouldn’t be much of any tds after ro.

Good thing to check - thank you!

 

[lmfbs]

My rejection rate is fine. Hers lacks a little. But not so much she should worry. Unless, she uses a lot of rodi. In which case a tune up is needed. I essentially say that.

Yeah - it seems like I'm going to be making quite a bit more water than you. Also, with an initial TSD so relatively low, this seems much higher than what I'm used to/what I'm expecting.

 

[lmfbs]

Your system is operating as designed. The RO membrane is where you'll see 90%+ of the filtration happen in an reverse osmosis system. The prefilters don't do much besides protect the RO membrane from failing prematurely.

The one thing that might need some attention is your rejection rate. The RO membrane should be able to remove 90%+ of solids in the water. So if the water going into the membrane is 52 ppm TDS, the water coming out should be 5 ppm TDS or lower. Check the water pressure going to the unit, and check the pressure between the prefilters and the membrane to make sure they're not clogged.

Also check the flow restrictor. Many manufacturers put comically undersized restrictors on RO units to make them more "efficient." The actual result is that the membrane is choked for brine and can't filter water properly. Most membranes are designed for a 4:1 brine to permeate (waste to product) ratio.

I left it running overnight and replaced the pre-filters, and now it's down to 4 or 5, which is more like what I was expecting. I'll attach the DI stage and see how we go. Thanks - this is helpful.

 

[Buckeye Hydro Verified Sponsor]

That's still only a 93% rejection rate - your membrane could be doing much better. Are you starving the membrane for pressure? What does your pressure gauge tell you?