Question for AWI - RO holding tank effect?

[wade]

I have one of your units with the RO holding tank on it (and RO drinking water diversion).  

 

I get the following parameters when I check it on my digital TDS meter:

 

input water (tap, ~60F, 40psi) is 250

RO outlet is 30-40

 

The problem is that I go through a full 10" DI resin column in only about 50-100 gallons of output based on the color change in the resin.  In order to use the product water for my reef topoff I have started draining the RO tank first (so everything is fresh from the membrane) and I use a new column.  The membrane is 2 months old, 75gpd.  This is VERY costly in terms of wasted water and DI resin.

 

Is having the RO tank slowly equalizing with the membrane input pressure causing this problem?  Is the RO water coming to equilibrium with the input water?  If that is the case, I am triply concerned as I have near the MCL for nitrates in my well water - and I have an infant in the house (not a good combination) - so if equilibration is occurring is it all ions that are equilibrating?

 

At this point I am considering a different unit so that I have one dedicated to drinking water and one to RO/DI output.

 

Thanks for any response!

 

 

 

[Air Water and Ice]

I understand your concerns Wade. I need to know what unit you have? The Bladder Storage tank is not meant to house RODI water. You have to think of the bladder tank as a bird bath and when the water sits it becomes stagnant and TDS will creep. Same as it would it if it was stored in a plastic trash bin, water sitting TDS will creep!

 

If you would perform the TDS test at the link below and let me know the results we can work from there. 

 

https://dl.dropboxusercontent.com/u/59844524/How%20do%20you%20do%20a%20TDS%20test.docx

 

I would need a last name to look at your order history with us and see what filters you are using to determine what other issues we might be having. 

 

If you would like, please email us at sales@airwaterice.com

 

or call us at 772-461-0256

 

Thanks,

 

Air, Water & Ice

[wade]

Thank you for the fast response!. I'll do a little more checking and get back to you via email/phone.

 

Cheers

[ctenophore]

Wade, I had the same problem a few years ago. I took the RO tank out. Now I flush the membrane prior to every storage tank fill. I get zero tds water and a gallon of di resin lasts me a year. I make 200 gallons of product water a month. I added a booster pump to increase membrane efficiency, so it's about 1.5:1 or 2:1 waste:product.

 

For drinking water, I just have a gallon milk jug that I reuse, and just fill it by hand at the storage tank tap. Lasts a few days between refills with 5 family members. I've thought about installing a faucet at the kitchen sink that connects to the storage tank, and just elevating the tank enough to gravity feed the kitchen faucet, but the milk jug hasn't proven enough of a hassle to warrant the major plumbing project.

[wade]

Thanks for the input.  I've replaced the membrane 3x in 3 years and unfortunately, I can't really figure out a way to use a smaller container for drinking water that wouldn't cause my wife to scream.  I am leaning towards stripping the DI carts off and just routing it as RO water only to the faucet.  Even 40 TDS is better than 250 (taste-wise) and since its for drinking, thats fine - unless it lets the nitrates through the membrane as well. Then it isn't OK at all.

[wade]

The unit I have is the Sku: 1DUALHR "DUal Home Reef with faucet and tank".

 

So shutting off the RO tank, flushing the membrane, and letting the lines flush brings my RO output down to ~13 TDS (from 230 at the tap).  A new DI column brings output to 0 TDS, but will have to see how long this column lasts.

 

I tested the shutoff valve and it is working fine (though I often wonder if equilibrating to 40psi is enough).  One thing I noticed, however, is that I shifted from a 50gpd to a 75gpd membrane without changing the restrictor, which I assume will have some effect on the membrane efficiency.

 

I will be ordering a booster pump asap, but it looks like I should be fine if I remember to shut off the RO tank and flush the membrane each time I want to generate tank water.

 

The only remaining question I have is the potential for nitirate to equilibrate across the membrane over time once it shuts off.