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Ion exchange softened water vs. RO water.


Forgive my ignorance, but I was of the impression that the RO process did produce almost
pure water with a neutral pH and near 0 ppm hardness. Thus the need for products like Kent's
RO Right to restore the water to a useable form, but minus the undesirable phosphates and
nitrates. I gather from your post that this is not the case, at least with regards to the pH
being affected.  Is that a correct understanding?   Because if that is the case, I would
certainly like to avoid the cost of buying an RO unit or bringing home RO water from the LFS
or grocery store.  It looks like using peat to lower the pH is a much simpler and less
expensive proposition.

As far as the plants softening up the water by using up the calcium and magnesium, in my
limited experience, that doesn't happen with much rapidity.  Where I previously lived in
Arkansas I was lucky enough to have water that was neutral to slightly alkaline (pH 7.0 to
7.2) and relatively soft at 70 - 80 ppm right out of the tap.   I performed 25% weekly water
changes and the water hardness in my heavily planted, CO2 injected, 80 watt Triton lit (with
polished reflector) 55 gallon never really changed off that reading.  Have you or others
experienced a significant softening of the water in your tanks by just the action of the
plants metabolizing the calcium and magnesium?  I could see this possibly taking place over
a long period of time if the water changes in the aquarium were limited or eliminated, but
not when I would be replacing 25% of the water weekly with additional hard water.  I doubt
the plants would ever be able to catch up to the point where the water would ever really
become soft, especially when starting with the VERY HARD water I have.

The water hardness here in my area of the upper midwest is in the 300-350ppm range, with a
pH in the 7.6+ range (the upper limit of my Aquarium Pharmaceuticals pH test).  I don't
really want to use water this hard in my tanks due to the deposits it tends to leave on
evaporation.  I would like to lower the pH to the 7.0 to 7.2 range, so I guess using peat
could do that, because even after softening, my water still has a pH in the 7.6+ range.

My main question still remains unanswered though.  Is the sodium in ion exchange softened
water detrimental to the plants or fish?  Can I use a combination of ion exchange softened
water and non treated hard water to reach my target hardness of less than 100 ppm and be
okay as far as the fish and plants are concerned?

I'm not sure if my local tap water contains phosphates or nitrates as I haven't gotten a
report yet from my local water utility.  I guess if it does I still may need to go the RO
route to avoid these algae inducing nutrients.

Which brings me to another question.  Is there any sort of consensus among the APDers as to
what an ideal target for pH and hardness in a planted aquarium is?  Or is there really no
standard as is my guess?


Jay Bickford
Savage, MN

> Date: Fri, 01 Jan 1999 08:43:30 -0800
> From: Steve Pushak <teban at powersonic_bc.ca>
> Subject: Re: Recommendations for a CO2 test kit?
> bickford at black-hole_com (Jay Bickford) asked about using tap water and
> ion exchange water to produce a given hardness.
> Jay, why don't you skip using the ion exchange water entirely and just
> allow your plants to soften the water by using up the nutrients? The
> problem with hard water is not the presence of the calcium and magnesium
> at all but rather the high pH caused by the presence of carbonates in
> water. Does RO water or ion exchange really do anything for the pH at
> all? Why bother? If you are fortunate enough to have water with lots of
> minerals and high alkalinity, you can simply use peat and CO2 to lower
> the pH a little. Or live with a slightly higher pH; its not that
> critical.
> Steve Pushak                              Vancouver, BC, CANADA
> Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
>  for LOTS of pics, tips and links for aquatic gardening!!!