View Full Version : Added my second Membrane

03/13/2010, 05:29 AM
Hi Jim,

Just wanted to thank you for taking the time to help me on the phone.

Here is the story and I will update the thread to my progress in water production...
I called Jim on Saturday 3/6/10 and asked for his opinion on how to improve water production from my current 75gpd RO/DI unit. I make a good amount of water and am getting tired of having to wait a couple days to get what I need. Jims suggestion was to add a second membrane, that will increase water production and decrease waste water. It sounded good to me so I went for it. Got everything in the Mail on Thursday and had it all hooked up by Thursday night. I have not needed to make water yet so when I do I will let everyone know if I noticed a drastic increase in water production.

Thanks again Jim and if I missed anything please share your thoughts.

03/22/2010, 11:31 AM
OK made my first large batch of water since adding the second membrane. It made 50 gallons of 0 tds water in 10 hours. You can do the math........

03/24/2010, 12:35 AM
We have tested dual membranes for over 4 years and have had excellent results. Waste water is low without using a constricting flow restrictor and chocking the membranes like other companys are doing. We feel we produce one of the best low waste high yield systems in the market today. we also sell conversion kits for existing 75 GPD membrane systems. If anyone has questions please call us 218 724-8000 and we will be happy to talk about what we sell with proven results.



04/04/2010, 07:47 PM
Jim, I have a question for you. When I added the second membrane I also changed out my DI with the stuff I got from you. It has already completely changed color and it looks like it needs to be changed again and its only been a few weeks. The TDS reading starts out like 2 then as I make water it goes back down to 0. What do you think? BILL

04/04/2010, 08:05 PM
Bill it soulds like your DI is on the edge of exhaustion and a steady reading of 2-3 is change time. How much water have you made and what is the tds reading of your RO water?


04/05/2010, 03:48 AM

I need to take another reading of the RO (thats the reading before the DI right?) don't know what that is off the top of my head. Whats happening is when the unit is off for a few hours and you start it back up the water comes out at about 7ppm then after it runs for a few minutes its back down to 0. The DI is almost completly changed color in about 3 weeks and I made about 400 gallons of water roughly....

04/05/2010, 07:44 AM
Correct the reading before the DI after the system has been running for five minutes. A tap water tds reading would be good also.


04/05/2010, 08:31 AM
I will get it tonight when I get home from work.

04/06/2010, 06:40 PM
OK Jim,

I left you a message to call me when you can. I tested the water after my sediment, carbon and carbon and get 187.....I tested my feed water and get 191.....I changed all my filters again including the DI resin and now my water out after the DI is 0 again. But I have a feeling in about 3 weeks the DI will be exhausted again. Not sure if I have something hooked up wrong or what. If you can call me when I am home and run thru how this thing is plumbed with me just to make sure I did not screw up that would be great....BILL

04/06/2010, 10:19 PM
After talking on the phone we determined the dual membrane system is plumbed correctly and the system is performing as expected. We suspect the municipal water system is currently on a well with low pH which is high in CO2. The tds after RO is running 1 to 2 or lower. High CO2 water can cause rapid DI exhaustion and doesn't have a tds reading. It is felt that testing the water will confirm low pH values. My suggestion is to run the system without DI at the present time and monitor tds readings.


04/07/2010, 03:31 AM
Thanks again Jim.....I am extremly happy with the increase in my water production. BILL

06/11/2010, 03:47 PM
Just found this thread...may be a solution to my problem too. I am not so much concerned about the time it takes to make the RODi water...but the waste water ratio 4:1 is killing me. My water bill is crazy. I have to find a way to improve this ratio with out spending a fortune.
My total system is about 250 gallons. So I am doing 50 gallon water changes every other weekend and about 20-30 gallons in top off water every week.

Will the dual membrane set up improve my ratio???
Could I plumb in a third membrane??

Sorry for the thread jack :hmm6:...but its kinda related.

Any help apreciated!

06/11/2010, 06:38 PM
No problem it will greatly help reduce your waste water. I forget the amount but it is drastic. It also depends on your water pressure the higher the pressure the better your results.

06/11/2010, 08:25 PM
Bigg D A dual membrane system will make a very big difference. Your waste will go from 4:1 down to 1 1/2:1 or less depending on your feed pressure. You will need at least 65 psi or higher or a system booster pump. Your tds in Atlanta is very good so the dual membeane should perform very well for you. If you are running a 75 GPD system now all you need to add is the conversion kit.




06/12/2010, 05:28 AM
This does indeed look like the direction I need to go.
With reguard to what kind of system I have, I got it second hand and it has a 100 gpd membrane.
Does the membrane determine what kind of "system" I have?
Can I change to dual 150's??

06/12/2010, 09:26 AM
Membrane size just tells me what yout rejection rate is. 100 GPD membranes only have a 90% rejection rate for tds. In Atlanta the poor rejection rate doesn't mean much due to your low tap water tds but you do have seasons where your tds does move up.

In my opinion Dual Filmtec 75's perform best and with higher pressure or a booster pump will out produce capacity. On the otherhand dual 150's almost always need a pressure pump and do not out produce capacity even at high pressure. You must have matching membranes for best performance.


06/13/2010, 09:22 AM

I just did an accurate measurement of my waste water. I made 1 quart of RO water and counter out like 17 quarts of waste water.

Any suggestions?

Could I have my system plumbed incorrectly?

06/14/2010, 11:34 PM
It is possible your pressure is low or you have the wrong flow restrictor? Look at our instructions page for drawings of plumbing details.