deionization

[rick rottet]

1) Do DI resins (seperated anion/cation beds) remove a general set of ions? What I'm really wondering is are there ion specific resins? For example, lets say my source water has high calcium and I want to leave that in (or any other desired chemicals).

2) If I posted my towns water report (11 prameters) and the EPA report of my towns water (37 parameters), could you recommend a filtration system? I could go to a manufacturer I'm sure but they will all try to convince me that their systems are the best for my application, I'm also sure -or is it just a general statement to say that RODI units are the best and thats it?

The reason I ask is because RO units waste alot and that may not be a big concern when making water for my forty gallon tank, but if I had a big venture in the works where I would need say 5,000 gallons a month, that would be a bigger expense to waste 5,000 to 20,000 gallons to get 5,000.

Thanks for your consideration.

[beaslbob]

just my $.02 here.

Ro/di will remove calcium, magnesuim, and calcium carbonate (calcium again?) from the tap water.

To me what is important is the makeup of the water in your aquarium which depends upon more than the water you put into it. I emphasize the tank itself processing the water. So I use tap and plant life.

I do agree the ro(/di) units waste a lot but that should not be a big expense or concern. To me a more important consideration is the effort required to process the water. At 20 gallons/day it takes several days to generate a tankful of water.

Just my thoughts. Perhaps Randy will come back from vacation and share his insite.

[Randy Holmes-Farley]

Do DI resins (seperated anion/cation beds) remove a general set of ions? What I'm really wondering is are there ion specific resins? For example, lets say my source water has high calcium and I want to leave that in (or any other desired chemicals).

There are no ion specific reasins that you are likely to encounter or that would be useful for you in this application (although some can be made at high cost, and I have done so for other industries). Any resin that you buy for an RO/DI will take out all cations, all anoins, or all of both kind, depending on what type it is.

Here's my article on tap water. My biggest concerns are chlorine, chloramine, and metals ldlike copper (that may come from your own pipes). RO/DI is the best system for tap water to aquarium water conversion, IMO.

Tap Water in Reef Aquaria
http://www.advancedaquarist.com/issues/jan2004/chem.htm


If wasted water is a big concern for you, then a striaght DI can work, but will cost aobut 10-20 times as much in DI resins as an RO/DI.

[rick rottet]

Thanks for your valued input. How expensive are you talking about? hundreds, thousands, hudreds of thousands?
Straight DI does remove those metals such as copper-right?
Can't DI seperate bed resins be "recharged" with strong acids and bases? (Save expense and waste of RO membranes). Another concern is the speed at which purified water is made. I may need to run mutiple RO/DI units to get 5,000 gallons of water per month. With a straight DI I could make hundreds of gallons upon demand. I just want to assure myself that a straight DI would have the same quality without the RO. Is the only reason to run RO before the DI is to save the longevity of the resins?

[Randy Holmes-Farley]

Yes, a straight DI does remove copper and all other ions. It does not remove chloramine, chlorine, or uncharged organics. Unless you are in a very unusual circumstance, you are probably best off relying on the decisions made by hundreds or thousands of folks before you with the same issues, usually ending up with RO/DI as the best choice.

My suggrestion with a need of 5,000 gallons per month is to talk directly to folsk that make and sell such units. Spectrapure, GE, and those that you can find by searching on the web for medium volume water purification systems.


Thanks for your valued input. How expensive are you talking about? hundreds, thousands, hudreds of thousands?


That depends on what you want to do, but they are not usually sold for tap water purification. I co-invented one for binding phosphate in people's intestines (Renagel), and it is a dollar or two per gram.

Is the only reason to run RO before the DI is to save the longevity of the resins?


It is not the only reason, but it is a big one. You'll still need carbon to remove chlorine and break down chloramine.

[rick rottet]

So, just to be sure my thinking is not too far askew; if I run a particulate filter or two, then a carbon block or two then through a seperated bed DI (and recharge the DI resins when necessary), I might be saving money over using an RODI say over a five year period (the expected life of an RO membrane) and still get comparable water quality?

[Randy Holmes-Farley]

You will get suitable water quality. I do not know if it will be cheaper or not. :)

FWIW, I've never had any problems with my 9 year old RO membrane.

[rick rottet]

Thanks again for your input. Really a wealth of knowledge.

[Randy Holmes-Farley]

You're welcome.

Good luck and let us know what you end up with, and how it works for you. :)

[JoeMack]

Randy. My RO/DI reads 0. If I was getting a 1-2 could that mean that my GAC could be exhausted (and not the DO) and is not catching the chloramine or does the RO filter that out? I know chloramine can hurt the membrane. Thakns

[jdieck]

Many Coral Farms that do not have access to natural sea water use sediment filtration, activated carbon and regenerable DI cartridges. There is work and $$ involved in the regeneration and replacement of resins so there is a break event point where the volume of water saved will compensate for the $$ cost.

At the volumes we use in aquariums disposable cartridges are still the most economical and trouble free.

[Randy Holmes-Farley]

Joe:

A properly functioning DI will take out anything that contributes to measurable conductivity. A value of 1-2 ppm TDS can just be noise in the measurement, or CO2 from the air getting into the purified water and ionizing to H+ and HCO3- that conduct electricity.