Looking for general RODI advice

Ztous · Feb 1, 2025

Hi guys, I've been in the hobby about 12 years but have let things slip the last few years and I am trying to get things back in order. I was checking on the TDS and the resin had likely been exhausted for LONG time. Was running at 18 after the membrane when I finally checked. I recently did a complete filter swap on it. It's 5 stage 1 micron sediment filter, 5 Micron Carbon block, 5 micron carbon block, RODI membrane tsw 1812 tw30 100hr then exhange resin in the small clear housing that I packed myself with resin that I purcheased off amazon called awesome aqautics. 800 flow restrictor on waste line. All stages were flushed sequentially upon install. I think the old filters and membrane were around 3 years old maybe a year older. Everything is automated so I kind of just forgot about it while alot was going on in my life.

I have 117 TDS going in and I am at 7 tds going into the exchange resin. Not sure what Pressure it is exactly but it's cold water going in. I am producing 4 cups of waste water for every cup of clean water. I have exhausted about a third of my resin making around 50 gallons of water and that rate of depletion isn't meshing with what I remember seeing in the past. I'm sure I didn't have to change the resin that often. I purchased this unit around 9 years ago and while it seemed like a good unit at the time when I look now it seems like the bar has risen and I'm looking for some advice on how to upgrade this system to get better performance. The new top of the line systems seem to have pressure gauges pre membrane, booster pumps and TDS meters inline with the flow along with more stages.

I am going to add a pressure gauge pre membrane to see what I am getting pressure wise I just need to grab one from work and make an adapter. I think I'm going to get the inline TDS so that I know whats going on. I also have another filter chamber sitting idle from a media reactor I purchased then seperated that I could add to this system and was wondering how I should best use it. I have never changed the flow restrictor. Just looking for advice on how to make this system more robust. Is the booster pump worth it? Should I add a stage? Despite the fact that it has always been a 100GPD I don't actually care how much I produce as long as I don't have to swap resin as much. This is also diffrent resin then I ran in the past and I am unsure if resins deplete at diffrent rates.

Any help would be greatly appreciated.

JumboShrimp · Feb 1, 2025

Just jumping in one on aspect of your question, I think you'd love a booster pump. Mine helps make water f-a-s-t.

Gtinnel · Feb 2, 2025

Your rejection rate is currently about 94%, which for a brand new DOW membrane isn’t that good, especially if the water is very cold which generally increases your rejection rate.
The pre filters do basically nothing to reduce your waters tds, they’re there to help increase the life of the membrane. On my system the tds is slightly higher after going through my sediment and carbon stages. You can add another stage but don’t expect it to decrease your tds after the membrane.
I have never used the brand of resin that you bought (and I don’t know if some brands last longer) but I wouldn’t expect it to be 1/3 depleted after only 50 gallons at 7ppm. You said your system is automated, so does this automation cause your system start frequently and run for short amounts of time? If so that will deplete resin quickly due to tds creep, if the initial water that is produced is sent through the resin, because the initial water will have a significantly higher tds.
Higher pressure is great for a rodi system, but may not be needed for your system if your homes water pressure is high enough. Getting a pressure gauge is probably a pretty good start.

signal7 · Feb 2, 2025

I'm also curious about the frequency and volume when running your RODI unit and potential TDS creep. Filling up a larger reservoir less frequently will help. I'd also question the quality of the resin. I see some reviews stating it doesn't last long, but that's situational as well.

+1 for adding a pressure gauge and maybe additional inline TDS sensors to better understand your situation and go from there. It's a small cost that will help tune your system, and you'll always use them.

Long-term, I agree with JumpShrimp about the booster pump. You can dial in the optimal pressure that way. Best thing I did was to add a second membrane and an Aquatec booster pump with auto flush. Something to think about.

Ztous · Feb 9, 2025

My system doesn't typically stop and start often, there is a ball valve for the water in and it goes to a 60 gallon food barrel with a float I run it dry then open the valve to refill the barrel but I do turn off the ball valve due to a general mistrust of the float valve. A barrel of water lasts me a long time when I am not doing water changes. Multiple months in the winter, But also the values listed were directly after the flitler swap and me refilling the barrel the first time so one straight run.

I have purchesed an inline TDS meter and installed it. According to it's readings after a few minutes or so of my RODI being pressurized my TDS is going to 1 ppm, when I was taking my sample before I never let it run that long. It whent from about 23ppm fast dropped to 7ppm then whent down over a minute or two to 1ppm. I had left it off for days at this point so I beleive that in rush is to be expected.

I have not installed the pressure gauge yet but 1ppm after my membrane seems fine. The guage should come in the next day or so.

The resin I used seems to have pretty poor reviews related to depletion so maybe something is amiss there. I was buying my resin from a local fish store and at least based on price it may have been higher qaulity. For now I will try a new resin and move forward.

Justdrew · Feb 9, 2025

Gtinnel said:
Your rejection rate is currently about 94%, which for a brand new DOW membrane isn’t that good,

It was always my understanding that the Dow 100gpd membranes were in that 94%-96% range. The 75gpd membranes reject 98%-99%.

Gtinnel · Feb 9, 2025

Justdrew said:
It was always my understanding that the Dow 100gpd membranes were in that 94%-96% range. The 75gpd membranes reject 98%-99%.

According to DuPonts website it tests at 98% under normal testing conditions. Most places that I see rate it from 96-98%

FilmTec™ TW30-1812-100HR

FilmTec™ TW30-1812-100HR Elements for home drinking water treatment units produce 100 GPD (15.8 L/h) of permeate with 98% stabilized salt rejection at standard test conditions. They are the most reliable and consistent elements in the industry. They are shipped dry for convenient handling and...

www.dupont.com

Buckeye Hydro · Feb 12, 2025

Ztous said:
Hi guys, I've been in the hobby about 12 years but have let things slip the last few years and I am trying to get things back in order. I was checking on the TDS and the resin had likely been exhausted for LONG time. Was running at 18 after the membrane when I finally checked. I recently did a complete filter swap on it. It's 5 stage 1 micron sediment filter, 5 Micron Carbon block, 5 micron carbon block, RODI membrane tsw 1812 tw30 100hr then exhange resin in the small clear housing that I packed myself with resin that I purcheased off amazon called awesome aqautics. 800 flow restrictor on waste line. All stages were flushed sequentially upon install. I think the old filters and membrane were around 3 years old maybe a year older. Everything is automated so I kind of just forgot about it while alot was going on in my life.

I have 117 TDS going in and I am at 7 tds going into the exchange resin. Not sure what Pressure it is exactly but it's cold water going in. I am producing 4 cups of waste water for every cup of clean water. I have exhausted about a third of my resin making around 50 gallons of water and that rate of depletion isn't meshing with what I remember seeing in the past. I'm sure I didn't have to change the resin that often. I purchased this unit around 9 years ago and while it seemed like a good unit at the time when I look now it seems like the bar has risen and I'm looking for some advice on how to upgrade this system to get better performance. The new top of the line systems seem to have pressure gauges pre membrane, booster pumps and TDS meters inline with the flow along with more stages.

I am going to add a pressure gauge pre membrane to see what I am getting pressure wise I just need to grab one from work and make an adapter. I think I'm going to get the inline TDS so that I know whats going on. I also have another filter chamber sitting idle from a media reactor I purchased then seperated that I could add to this system and was wondering how I should best use it. I have never changed the flow restrictor. Just looking for advice on how to make this system more robust. Is the booster pump worth it? Should I add a stage? Despite the fact that it has always been a 100GPD I don't actually care how much I produce as long as I don't have to swap resin as much. This is also diffrent resin then I ran in the past and I am unsure if resins deplete at diffrent rates.

Any help would be greatly appreciated.

Give us a call when you are in front of the system and we can help you get that system squared away.
Russ