2 - DI vs 1 - DI

[FranktheTankTx]

I have a BFS RO/DI 4 stage unit which gives me 0 TDS. However, I have noticed some reefers are running 5 stage units - with 2 DI housings.

Any particular reason? I could always add another DI housing on to my current unit if there is an added benefit.

[downhillbiker]

as far as i know, the 2 stage dont do anything more. you get 0 TDS out of a single stage. that said, when i bought mine it was the same price for 2 stage as 1, so i bought the 2. people say you can just rotate the second stage into the first spot when the other one is worn out, then fill the other one up, and put it in the second stage.

[schneijt]

Two-stage DI is used by a system from Spectrapure with two separate types of DI. The first DI is a "roughening" DI stage that greatly extends the life of the second DI. By using the two stages available from Spectrapure, you can run an incredible amount of RO water through your DI before needing to replace either stage. I'm not 100% sure how it works, but AZDesertRat is the guy to ask about RO/DI and Spectrapure. If you're using two "regular" DI stages, there's really no benefit. You'll double your DI life, but you're using two cartridges... No rocket science there. :-)

-Joe

[AZDesertRat]

What some people will do is run seperate cation and anion DI stages so they can recharge their own resin. I don't recommend this myself since it takes acid and lye to recharge resins and both can be tricky to work with. I get enough chemicals at work, I don't need stuff like that around the house for the Grandkids to get into.
Spectrapure does it differently with their MaxCap DI cartridge. It is a pre DI if you will which extends the life of the downstream DI cartridge by at least 3.5x and gives true semiconductor or nuclear grade water of 18.2 megaohms resistivity. My DI lifewent from 150 gallons per 20 oz cartridge to over 800 gallons per cartridge so I won't use anything else. I have tried bulk resin from every source imaginable, most of them here on RC and others and nothing is even close.
If you want to run two normal mixed bed resin cartridges what you do is put a dual inline meter between the stages and after the last one, when you start to see TDS out of the first cartridge move the last one into the first position and add a new one to the end, this makes DI last longer and work better.

[ChuckLawson]

<a href=showthread.php?s=&postid=13556860#post13556860 target=_blank>Originally posted</a> by AZDesertRat
If you want to run two normal mixed bed resin cartridges what you do is put a dual inline meter between the stages and after the last one, when you start to see TDS out of the first cartridge move the last one into the first position and add a new one to the end, this makes DI last longer and work better.

+1 -- I do this, but I don't keep a meter between them; I just use color changing resins.

[AZDesertRat]

Color changing resin is a really poor indicator of condition. Often its past due to be replaced before it has turned colors, other times it turns and is still good. I would never rely on color changing resin for anything. Get a TDS meter and you will see exactly what I mean.