TDS after sediment and carbon

[DeniableArc]

G’day reefers, I have the following
0.5 micron sediment
Booster pump
2x 0.5 carbon
75gpd membrane
2x di cartridges

My question is my supply water is 100tds and after sediment and 2 carbon blocks it between 70-80 TDS is this normal?
TDS after ro membrane is 2 and after the first Di cartridge is 0.
Is it normal for RO membrane to do Majority of the TDS reduction?
All filters only months old and maybe 300litres through them

 

[Saltyreef]

Yes sediment and carbon do very little for tds removal.

 

[Randy Holmes-Farley Verified Community Expert]

TDS is not expected to drop after those filters, and can even rise after the carbon filter, for example, by breakdown of chloramine. The sediment filter does nothing for TDS.

 

[Buckeye Hydro Verified Sponsor]

As an aside, suggest you move your booster pump to a location AFTER all your prefilters.

Russ

 

[Courtney Aldrich]

G’day reefers, I have the following
0.5 micron sediment
Booster pump
2x 0.5 carbon
75gpd membrane
2x di cartridges

My question is my supply water is 100tds and after sediment and 2 carbon blocks it between 70-80 TDS is this normal?
TDS after ro membrane is 2 and after the first Di cartridge is 0.
Is it normal for RO membrane to do Majority of the TDS reduction?
All filters only months old and maybe 300litres through them

Yes, this is correct. Most water supplies are >100 TDS and the RO membrane does most of the work (these membranes are amazing!). The sediment filter just removes fine particulates while the carbon removes dissolved organics and chlorine. The DI cartridge removes any residual salts to give you 0 TDS water. I believe Sidney uses chloramines, so make sure you have the proper carbon filters.

 

[vic5hands]

Question ? So with a 3 probe RO meter at what reading does the Membrane filter require replacement

 

[Courtney Aldrich]

Question ? So with a 3 probe RO meter at what reading does the Membrane filter require replacement

Most manufacturers recommend replacing the RO cartridge when the rejection rate falls below 85%. So if you start with 80 TDS water into your system, when the TDS increases beyond ppm after the RO filter, then I would change the membrane - the rejection rate in this scenario is [(80 - 12)/80] x 100 = 85% . You'll know when to change the sediment filter when the system pressure begins to drop. The carbon filter for removal of chlorine can be checked by measuring for chlorine in the purified water using many kits or test strips. The cartridges are very inexpensive, so I think it worthwhile to change these more regularly than many people report (I've seen threads here where people don't changes their filters for 3+ years).

 

[Opus]

Question ? So with a 3 probe RO meter at what reading does the Membrane filter require replacement

Most are rated for 98% rejection rate or better with a guarantee of 95% or better. Most would recommend changing the membrane when it drops below 95%. I have a 99% rejection membrane and I plan on changing it when it gets below 99%. Currently my tap water tds is over 400 and it is 4 to 5 after the membrane. Unless you make a ton of water or you let chlorine get to the membrane and ruin it, you should get 5+ years out of it. My ro unit is 25 years old and I'm on my 6th membrane.

As others have stated, the prefilters are not there to lower tds, their main job is protecting the ro membrane.

 

[Courtney Aldrich]

Most are rated for 98% rejection rate or better with a guarantee of 95% or better. Most would recommend changing the membrane when it drops below 95%. I have a 99% rejection membrane and I plan on changing it when it gets below 99%. Currently my tap water tds is over 400 and it is 4 to 5 after the membrane. Unless you make a ton of water or you let chlorine get to the membrane and ruin it, you should get 5+ years out of it. My ro unit is 25 years old and I'm on my 6th membrane.

As others have stated, the prefilters are not there to lower tds, their main job is protecting the ro membrane.

Thanks for correcting based on your extensive experience. I love these forums since I can speculate and when I'm wrong, I get quickly corrected and learn something new.

 

[Opus]

Thanks for correcting based on your extensive experience. I love these forums since I can speculate and when I'm wrong, I get quickly corrected and learn something new.

Thanks, and yes we are always learning. But as always we shouldn't base our opinion on one anonymous opinion on a bulletin board. I do try to research major issues.

Take flushing the ro membrane. Some will recommend that it be done every time you make ro water because it will prolong the live of the membrane. After researching I've concluded at this point it is not something to be done. There is no proof that it actually does, it is just a theory. It probably does to a point, but unless you can show that it prolongs it for a period that is long enough to justify all the time and water used in the process, then I'm not doing it. Adding 1 month to the life of the membrane, which should last 5 or more years, is not worth it. If you are adding a year to the life of the membrane, then I would do it.

 

[snvadher]

What should be the expected value for home RO after passing water through Membrane, my tap water TDS is 460, and at the end when entire cycle completes I get TDS around 10-11. it it OK?

 

[KStatefan]

What should be the expected value for home RO after passing water through Membrane, my tap water TDS is 460, and at the end when entire cycle completes I get TDS around 10-11. it it OK?

That gives you a rejection rate of of 97.5%. Which is good depending on your membrane specs.

 

[snvadher]

That gives you a rejection rate of of 97.5%. Which is good depending on your membrane specs.

Thanks

 

[Buckeye Hydro Verified Sponsor]

Unless you make a ton of water or you let chlorine get to the membrane and ruin it, you should get 5+ years out of it.

The other primary killer of RO membranes is hardness. Just like hard water will deposit scale on your faucets and showerheads and such, it will deposit scale inside the RO element and plug the semipermeable membrane layer.

So in response to the question from customers "How will I know when my membrane needs to be replaced?" our answer is:
You'll see one or both of the following - permeate not as clean as it should be (as measured by a TDS meter), and or production slower than it should be after you adjust for your pressure and temperature. Slower than expected production is due to scaling (or, less commonly, fouling).

Russ