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Re: RO vs. DI (was APD V3 #1162

Hello Andrew,

First of all, you did not say WHY you want to treat your water.
Second, do more investigating before deciding on DI vs. RO.

The "Tech Rep" who told you that the capacity of the ANI/KATI resin
columns is 2000 gallons, is full of air! Capacity of an ion exchange
column is NOT measured in volume units (except in specific cases) but in
mol equivalents or weight (usually of CaCO3).

Using an ion exchange resin bed, one can process 10 times the volume of
water of 20 ppm hardness, than water of 200 ppm hardness! Same goes for
anions. Thus column capacity in volume units is meaningless. So, if a
sales person gives you such attractive, but inappropriate figures, you
can draw your own conclusions about their veracity...

There have been reports in the German aquarium literature that water
that stands in a column overnight leaches something deleterious from the
column and has to be discarded. Its not so much the volume of water
lost, as the bother.

Recharging is NOT complicated, but it is quite a chore! 

I am not certain whether ANI removes all phosphates effectively. 
Phosphate comes in many forms and I would guess that many of them are
not removed by an ion exchange column. Be specific in your questions and
insist on something in writing.

Reverse osmosis is NOT a panacea either!

Most important, in RO there is that "wasted" water. I put wasted in
quotes, because one can use that water for watering the lawn, gardening,
or growing Daphnia.

Second, you will never get a total removal of any ion. But would, say,
90% removal of phosphate be good enough? Also, large organic molecules,
pathogens, etc. get removed by RO, but not by DI.

If you estimate, that 2000 gal will last you two years (i.e. about 3
gal/day) -- why are you concerned about RO's 50 gal/day flow capacity? A
10-gal/day unit would serve you just fine!

As I said before, decide WHY you want water treatment, WHAT you want to
accomplish -- and then carefully select the method, based on hard facts,
NOT a sales person's "opinions".



> Date: Tue, 20 Jul 1999 02:06:28 EDT
> From: BOLLING37 at aol_com
> Subject: KATI / ANI   vs.  RO / DI
> Hello all,
>      I just got off the phone with a tech rep at Pet Warehouse.  I wanted to
> know
> if the ANI (anion removing DI filter) could be used by itself to remove PO4
> from
> my tap water.  He didn't really have an answer, but recommended that the ANI
> be
> used with the Kati, (the cation - removing unit, designed to be used together
> to
> produce pure water) which will cost me ~ $229.(Both units) I can get a Kent
> Marine RO/DI Maxxima unit for the same price, but I'm not sure if Kent resins
> can be recharged?
>      The Kati/Ani solution has a few advantages:
> 1.  Both can be recharged with HCl (Kati) and Sodium Hydroxide (Ani)
> (And yes they are nasty, caustic compounds, but wearing goggles, gloves, and
> an
> apron should do the trick)  The Kati 2 (the larger size) is rated at around
> 2000 gallons between recharges, which will last me ~ 2 years before I need to
> reach for the acid.
> The Ani 2 is similar.
> 2.  Can produce up to 360 gallons per day. (The Kent RO unit mentioned above
> can
> only produce 50 gallons per day)
> 3.  No Wastewater!!  The RO units dump 4 - 6 gallons of wastewater for every
> 1 gallon of pure water produced.  What a waste.  I don't live in a water -
> restricted area like certain areas of CA, but why waste water if you can help
> it?
> (I suppose I could always save the water and use it in the garden)
> Disadvantages:
>      I'm not aware of any, perhaps someone out there is?
> The only possible disadvantage I can think of is:  After the unit is
> recharged, the first 12 gallons of water are thrown out. (I'm guessing this
> is to wash out any residual amounts of caustic soda or HCl left over from the
> recharge procedure)
>      I would like to use the Ani unit alone, to remove PO4, but even though
> he(the tech rep) didn't recommend doing this he couldn't give me a specific
> reason either.
> I do know that Kent Marine does not recommend using their DI anion - removing
> resins alone, because the life of the resin is reduced.  Why this is so has
> never
> been explained to me.  Any ideas?
> Thanks,
> Andrew  (In a somewhat cooler but still very humid Macon, Ga.)