R/O DI water

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baley

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Mar 12, 2005
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I have a 5 stage R/O unit I’m currently using for my saltwater tank.
I just purchased an add on DI unit for it and was going to hook it
up tonight. I assume it would go as the last stage of purification.
My question is, if I just used the DI unit, would I have to
de-chlorinate the water before I used it? I like the R/O water, but it
uses SOOOOOOO much water. Do you think its worth the waste
to use both until, or would DI be just as good as the R/O by itself.
Thanks for you time
 
That is a good question. The way I see it, the deion resin is rather expensive, It will however make water that is good enough for reef use by itself, however it will not last very long at all, and you will buy more, and more, and what happens if you dont notice it or let stay in just one water change to long. The ro membrane on the other hand, if you keep your prefilters clear will last for 1-2-maybe 3 or more years. The Di cartrige which is not having to work as hard now getting much purer water lasts for a reasonable amount of time, and since water is cheap, and di is not, I use my ro membrane. Hope this helps you. Steve
 
Thanks wrightme43.
I agree with you. I hooked up the DI unit to the RO unit last night.
I'm running the waste into a trash can and pumping it out with an
old mag 5 pump to water flowers outside.
Thanks again.
 
My question is, if I just used the DI unit, would I have to
de-chlorinate the water before I used it?


Are you sure it is chlorine in the water or chloramine ? Your RO unit more than likely has a carbon filter in it. Chlorine and/or chloramine react with carbon in the carbon filter and yield the following equations

1. NH2Cl + H2O + C* => NH3 + Cl- + H+ + CO*

2. 2NH2Cl + CO* => N2 (g) + H2O+ 2H+ + 2Cl- + C*

(C* and CO* represent carbon and carbon oxide surface (of activated carbon) respectively.

Note that in the reduction of free aqueous chlorine by AC only H+ and Cl- ions are generated:

3. C* + HOCI => CO* + H++ Cl-

4. C* + OCl => CO* + Cl-



Activated carbon removal of chlorine by catalytic reaction.

2ClO- > < C > > O2 + 2Cl-

So in short, the chlorine and chloramine are converted into chloride ions. They are harmless and make up 19 ppt of seawaters 35 ppt.

For further reading
Chloramine and the Reef Aquarium
http://reefkeeping.com/issues/2003-11/rhf/feature/index.htm

Next months reefkeeping.com article is going to be on RO/DI systems, with info on carbon and it use on removing chlorine and chloramine, in RO/DI systems.

One of the good things about a DI is the RO does very poorly at removing some ions like silica.

Water lose in RO's can be reduced greatly by increasing the line pressure up to 125 PSI, but one needs a different membrane for this. Such systems also require a special positive displacement pump to increase the line pressure. Such units are pricy and usually produce more RO than you would want. Most of the hobby RO's have a Recovery Rate (water saved) of 4-1, which means for every gallon of RO 4 gals is wasted. High line pressure units bring this down to 2-1 and the Rejection Rate ( ions removed) is also increased ( purer water).
 
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