half DI

[rick rottet]

would there be any predictable negative effects to using only the ani portion of a separate bed deionizer? (this would be after an RO)
my tap has high levels of iron, calcium, and magnesium. i use an iron removal system, but why remove the calcium and magnesium...granted i would test to see that they wouldnt become excessive. what other post-RO + ions might be considered undesireable?
it seems that many of the undesireable compounds are - ions (phosphates, nitrates, silicates,.....), and many desireable ones are + ions (calcium, magnesium, ....) hence the thought to use only the ani.

[bertoni]

Well, copper and zinc are both cations, and I'd prefer them to be removed, so I'd use both phases. Also, calcium and magnesium from tapwater aren't always desireable, depending on the salt mix and the consumption rate of the tank.

[raaden]

To get to the question the ones that would concern me are Cu and Zi as listed below, but also Pb, Li, Cs, Hg (this is a big one if you have it in your water), and Ag. These are all things I would want to get out of the water.

I looked into almost the same thing about a month and a half ago, as I have a similar high iron level (although not quite as high as yours ) in addition to some other things. After talking through a couple of different setups with the company that did my water analysis we came up with 2 considerations.

1. If you use an RO you are going to strip out most of the heavy metals anyway, which would be a good thing, but you are also going to strip out most of the calcium, magnesium, and strontium (97-99% depending) as well, so the gain would be minimal.

2. Depending on the levels of the source water you can get different types of metal reducers that will strip out all but the alkali earth metals (Ca, Mg, Be, Sr, all of these are very good to have), but this leaves you with Barium and Radium which would not be good to have concentrating in the tanks if you have these minerals in the ground. And this type of solution is very, very expensive. Much more than using a 2 part to add back what you want.

So I believe I am back to using an RO with a Kati/Ani 10. Unless someone else has some ideas.

[WaterKeeper]

In a commercial softener used for mainly anion removal we still run the water through a sodium exchange cation resin before the anion. Why, well the calcium and magnesium. generally the most common cations in tap water, form insoluble hydroxides inside the anion section if not removed before hand. This fouls the resin and severely limits its production. You wouldn't want to do this with a reef tank however as it would raise sodium levels over time. I'd run a total exchange myself over selectively removing anions. It will save money in the long haul.