# RODI Efficiency



## CamH (Jan 5, 2014)

Wondering what ratio of waste to product people are getting out of their RODI systems? I know that temperatures effect speed but it shouldn't change the output ratio. I keep water in a 20G brute and it seems to take more than 8 hours to fill. I tested the output ratio today and found that I was getting a 13:1 ratio. I tested this by timing how long it took to fill one measured cup. It took 7.5 secs to fill with waste water and 96 secs with RODI.

Is this normal? Seems a bit excessive


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## 4pokguy (Apr 27, 2011)

13:1 is definitely excessive. The instructions for my RODI filter say the ratio should be 3:1 (waste:filtered).


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## CanadaCorals.com (May 12, 2013)

3:1 or 4:1 (rejection/production) is standard.

With a boost pump, efficiency increases closer to 2:1.


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## blunthead (Jan 24, 2011)

yup, somethings not right


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## badmedicine (Oct 27, 2012)

Just my guess:
What water pressure is your unit working at? I ask this because the RODI requires water pressure to pass the RO membrane. Too low and the water will flush down the drain. Too high and it could damage the membrane.

This is not a big problem as their are pressure boost pumps and limiters to equalize the pressure.


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## CamH (Jan 5, 2014)

The pressure gauge reads 60psi


Sent from my iPhone using Tapatalk


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## cica (Feb 10, 2013)

Do you have a needle valve or a fixed flow controller on the waste water line? If it's a needle valve then you can adjust the ratio of RO / waste water by closing slightly the valve.


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## blunthead (Jan 24, 2011)

60 psi isnt terrible
which ro unit do u have?


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## CamH (Jan 5, 2014)

No needle valve. I have the Spectrapure CSPDI 90GPD 

I emailed Spectrapure and this is their response:

"No, as the water temperature changes the ratio will change; the ratio is constantly changing with the water temperature change due to the fixed brine rate but changing production rate. ressure is producing 60-GPD thus you should order a 60-GPD flow restrictor that will compensate for your water conditions. That will bring the ratio into the proper proportions.

If you have a ball valve, you could add that to the brine line and govern down the flow but make sure the valve never get turned to low.

The ratio will be lower in the summer but it may never get as low as you would like to see it.

There is a 3% rise in production for every 1 degree C increase in temperature (Obviously works in reverse too)"


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## skim (Apr 21, 2014)

In a perfect world you will get 3:1 many things affect water to waste water and one of the biggest is water temp so perfect world new system with min. 60 psi and water temp. of 77 F should get a standard 4:1 ratio. Now drop the water temp to 38 to 40 at this time of year and that ratio goes way up, just another good reason to get a booster pump. So do not panic your system is most likely fine.


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