Poor RO Performance (High TDS) - IceCap RODI Smart System

mstgkillr · May 7, 2020

I continue to experience poor RO performance (high RO TDS) from my IceCap RODI Smart System. I have already reached out to CoralVue several times over the last few months, with little to no help. Following their advice, I replaced the 75 GPD DOW Filmtec 99% rejection membrane (BW60-1812-75), 1 micron sediment filter, and 5 micron carbon block, with absolutely no change in performance.

I am just about to give up on this RODI system and go with something proven (SpectaPure, BRS) or at least supported. My previous RODI system that I owned prior to getting back into the hobby, a simple 4 stage system with booster pump always performed well under the same conditions at the same house. Any help would be greatly appreciated!

RODI System Source Water and Performance Data

SW Florida well water, with an aerator and high end water softener
Hardness to RODI system = <1 grain per gallon (excellent)
TDS to RODI is 550 ppm (should be mostly sodium due the water softener)
TDS after RO membrane is 20-40 ppm, depending on the flow restrictor used, but should be roughly 5-6 ppm
RO rejection rate is 92.7%-96.3%, when it should be 99%
Well water pressure is 40-60 psi, but the RODI booster pump brings it up to 80-90 psi with the 550 mL flow restrictor and 70-75 psi with the 800 mL flow restrictor
The 550 mL flow restrictor produces a 2:1 waste ratio and approximately 137 GPD of RO water, with a 35-40 TDS after the RO membrane.
The 800 mL flow restrictor produces a 4:1 waste ratio and approximately 97 GPD of RO water, with a 20-30 TDS after the RO membrane.

Water Dog · May 7, 2020

These are the details of the 75 GPD Dow Filmtec RO membrane copied from BRS...

DOW Filmtec 75 GPD Membranes have a 96% - 99% typical stabilized salt rejection rate that can be reproduced through the following conditions;

Source Water Pressure - 50 PSI / Membrane
Source Water Temperature - 77°F
Source Water TDS - 250ppm Softened Tap Water
Recovery - 15%
Minimum Salt Rejection - 96%

So when you’re using the 800ML flow restrictor and yielding the proper 4:1 waste ratio, while it’s on the lower end of the spectrum, it seems that your membrane is running up to the manufacturer’s spec between a 96 - 99 percent rejection rate based on your 550 TDS source water.

mstgkillr · May 8, 2020

It does appear that I am within spec, but just barely. In the past, I must have been at the higher end, because I do not ever recall a permeate TDS above 10 ppm.

So what do people do with even higher source water TDS, in the 1,000s. Do they just deal with a permeate TDS of 40 ppm and go through a ton of DI resin? Should I run another RO membrane, in series? It would get me down to <1 TDS. I know it would cut way down on production, but I have 75 gallon storage tanks.