DI exhausts after two water changes

[Tom Toro]

Any lead on a great DI resin that doesn't exhaust as quickly as most? On my r/o units and after a 2 50 gallon water changes and two weeks worth of evap, I need to change out the cartridge. My evap level is around 2.5gallons a day.

I have 357 going in, 4 going to the resin and 0 after the resin, but I'm changing every couple to three weeks. Is this about normal? I'm using brs nuclear grade color changer.

[Manoj's Reef]

I am by no means very good at this subject but will take a stab from what I have read so far.

The rapid depletion of DI is usually due to membrane being inefficient. Also pre treating the water before it goes in also helps. There was a thread on R2R on this subject.

[jimsflies]

How old are your membranes? 4 seems like a lot post RO. Do you have a carbon stage and how old is that?

[Tom Toro]

How old are your membranes? 4 seems like a lot post RO. Do you have a carbon stage and how old is that?

Both changed out last year, but I do have rough well water. I have whole house filter, softener and then the r/o units. I just changed the other four stages two weeks ago. I'm using the 75gpd tfm can't remember the brand.

[rmalone]

Whats killing you is that your not running the ro for 15-20min before sending it to the DI resin. When you first pressure up the ro membrane it will give 2-3gal of high tds water. On my membrane, which ends giving about 1ppm, it will start at about 140ppm and over the course of 15 min or so gradually drop to 1ppm. So if 1gallon of water at say 80ppm hits the resin it burns as much resin as 80g at 1ppm.

Spectra pure sells a nice little 2 way valve that lets you bypass the resin and just dump that initial high tds water.

[Tom Toro]

Whats killing you is that your not running the ro for 15-20min before sending it to the DI resin. When you first pressure up the ro membrane it will give 2-3gal of high tds water. On my membrane, which ends giving about 1ppm, it will start at about 140ppm and over the course of 15 min or so gradually drop to 1ppm. So if 1gallon of water at say 80ppm hits the resin it burns as much resin as 80g at 1ppm.

Spectra pure sells a nice little 2 way valve that lets you bypass the resin and just dump that initial high tds water.

That makes a lot of sense. I can bypass it myself with some valves. Also, if that's the case, then my ato water (5 gal bucket) is always wasting my resin since it only asks for about a half gallon at a time. I should make it gravity feed from a larger reservoir that I fill once a week.

Thanks for the help, Folks!

[dentdominator]

Hey Tom,

I had the same problem with the hard water in my house. I got tiered of changing the single DI unit frequently so I made a 4 stage DI unit and now it takes 3 - 4 months to exhaust the resin to 002 ppm. I've even gone longer up to 6 months and I think the meter read 005 ppm.

[MyNemesis]

If you have a RO Membrane flush bypass, you should flush the membrane for three minutes before and after every time you use the unit. As RMalone said, this saves the DI Resin. I have a meter before the DI unit and you watch it go down, then turn the flush off after it is at a low level. The guys at BRS told me the three minute deal and it really does help.

[Tom Toro]

Hey Alex,
Yeah, your setup is nice and automated. 6 months would be great! I'm switching it out every couple of weeks. I think you already do the large reservoir for top off, right?

John, I'll try the flush. I have it only one of my r/o units, but if it helps a little, I'll be happy.

[Flynnstone]

i myself am a little confused as why you would need to run the water for 3 minutes. would this be from algea that is living inside of the ro membrane housing? i dont believe anything can really leach through the membrane, so it must be from another source. my dual DI last for approx. 6-8 months, but the unit is in a dark closet. evap is at least 2 gallons a day, water changes are 50g monthly. top off water is being added every few minutes directly from the ro/di unit, maybe this is why it works well for me? moss dont grow on a rolling stone.