How tap water deionizer works

[kwyjibo]

Hi Randy,

I'm a noob and have been lurking around RC for a while.
Just wanted to say you have some great replies which I dont understand all the time, but it's great that you include so much detail.

Anyways, onto my question.
I searched around on RC looking for a discussion on the Aquapharm tap water purifier, but no one really talks about how it works.
I recently bought an oceanic 75G RR and it is a b***h to fill a tank with >50G of water(I have 100 lbs of southdown in there too).
I would hate to be one of those guys with the 180 or 210. Anyways, I have a Maxxima RO Hi-S system but waiting for a gallon of water from it is like watching paint peel off of a wall.
My impatience got the best of me so I grabbed two tap water DI units and hooked them up in series to the hose outside and water was now trickling into the tank rather than in droplets.
When I mentioned this to my big bro he said that my doing so was wasting the second cartridge.
He went on to explain that the simple flow of water thru the 2nd tap water purifier in series was wasting the media away even if the water was previously filtered in the 1st DI unit.
Prior to this, I thought that the DI media was static and water simply diffused through the media and dropped off the contaminants as it went through. I had no idea that the water would also displace the media at the same time.
Could you please point me to a quick summary on the aquapharm tap filter's inner workings?
And maybe even a little DI 101 for other noobs who havent taken biochem yet?

[Randy Holmes-Farley]

As you've always suspected, you are smarter than your brother.

The second DI will not be changed at all unless ions are leaking through the first one.

The way that these devices work is as follows:

You have a solid material that has positive charges permanently attached to it. Loosly attached to those positive charges are negatively charged hydroxide ions (OH-).

Similarly in the DI bed you have a solid material that has negative charges permanently attached to it. Loosly attached to those negative charges are positively charged protons (H+).

So suppose that you start with a solution with salt in it, as sodium (Na+) and chloride (Cl-).

The Na+ comes along and displaces an H+ from a negatively charged site. Taking up the new spot.

The Cl- comes along and displaces an OH- from a positively charged site. Taking up the new spot.

The released H+ and OH- combine together to form water (H2O)

So in the end, the salt is taken up and nothing except water is released.

If you only pass pure water through it, there is no possibility that the H+ and OH- will come off of the resins, so the resin is unchanged.

Hope that helps.

Just wanted to say you have some great replies which I dont understand all the time, but it's great that you include so much detail.

Thanks.