New RODI only 95%

[niccumec]

Installed brand new BRS 7-stage RODI pro 150GPD water saver with booster pump. And have run ~120 gal product, but I don’t think it is working optimally. Still only gets to 8ppm TDS after membrane. While I do get 0 TDS after DI, I am only getting 95% rejection rate after membrane versus the 99% advertised. Seems like this will just eat up my DI…. I also am getting more product than waste (see test below).

I did open up the membrane housings and inspect seals - all looks to be in order.

I performed a 15 minute bucket test with waste in one and produced in the other.
Inlet: 88 psi, 70 deg F
TDS: Inlet - 174 / post membrane - 8 / post DI - 0 (95%)

Waste: 306 oz
Produced: 344 oz
Ratio: 306/344= 0.89

Could water be bypassing the membrane causing higher TDS and lower ratio?

 

[Uncle99]

it could bypass and give you that result.
If passing membrane, it will exhaust your DI unusable fast.
Can also bypass DI same results.

But I have to run mine for at least an hour before I get zero.

I’d give it more break in time to be sure.

 

[Randy Holmes-Farley]

Any time the tap water is touching the ro/di membrane without flow, ions will creep across and eventually equilibrate on both sides. To do a rejection test, you need to discard this high tds water before starting collection. You may have done that, but if not, it can result in seemingly low rejection.

Low pressure can also lead to poor rejection.

 

[niccumec]

Any time the tap water is touching the ro/di membrane without flow, ions will creep across and eventually equilibrate on both sides. To do a rejection test, you need to discard this high tds water before starting collection. You may have done that, but if not, it can result in seemingly low rejection.

Low pressure can also lead to poor rejection.

I am reading TDS via inline probes after running continuously for an hour or so and my pressure is running at 88-90 psi.

 

[Randy Holmes-Farley]

FWIW, my system from Spectrapure only gave about 92% rejection based on tds, but I do not know what the specification claimed.

Rejection will depend on what is present, and substantial ammonia or silicate or CO2 will be more poorly rejected.

 

[Rjramos]

Those numbers are the same I get here in south Florida. TDS 165-170 tap, around 8 post membrane and 0 after DI. Filter companies tell you 95-99 purity following membrane, this depends on what the incoming tap water is. Around 6 months, post membrane TDS starts to increase into teens, I change out 1,2,3 and it slowly decreases back to 8, if it doesn’t come back down, it’s time to change the membrane, usually about 1.5 yrs. I have 2 back to back D/I canisters and these I change out at TDS 1. I start getting 1 about 3-4 months after changing 1,2 and 3