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CO2 and Water Softeners

Contents:

  1. CO2, Ph, and water-softener
    by 2392-at-tccn.com (John E. Rogers) (2 Apr 1995)
  2. CO2, Ph, and water-softener
    by (e-mail) (Erik Olson) (3 Apr 1995)
  3. CO2, Ph, and water-softener
    by ac554-at-FreeNet.Carleton.CA (David Whittaker) (Wed, 5 Apr 1995)
  4. CO2, Ph, and water-softener
    by gqva06-at-udcf.gla.ac.uk (Wilson Angerson) (Fri, 7 Apr 1995)

CO2, Ph, and water-softener

by 2392-at-tccn.com (John E. Rogers)
Date: 2 Apr 1995
Newsgroup: rec.aquaria

I have read with great interest the use of CO2 systems to enhance plant 
growth.  As for my own system, I figure it is both the lack of light and 
CO2 that may be slowing my plant growth.  I am currently changing my 55 
Gal. freshwater tank from two 15W tritons to two 40W tritons.  

My question is this...  I have been keeping my fish in water softened 
using a standard water softener(tank..salt..resin).  I mainly keep 
live-bearers, and while they probably preferred the hard water from the 
tap, they have not seemed to be too adversly affected by the soft water.

So.... what might I expect by adding CO2 to water treated with the 
water-softener?

While I want my plants to grow, I don't want to kill my fish in the process.

John Rogers (2392-at-tccn.com)


CO2, Ph, and water-softener

by (e-mail) (Erik Olson)
Date: 3 Apr 1995/1996
Newsgroup: rec.aquaria,sci.aquaria

2392-at-tccn.com (John E. Rogers) writes:

>I have read with great interest the use of CO2 systems to enhance plant 
>growth.  As for my own system, I figure it is both the lack of light and 
>CO2 that may be slowing my plant growth.  I am currently changing my 55 
>Gal. freshwater tank from two 15W tritons to two 40W tritons.  

>My question is this...  I have been keeping my fish in water softened 
>using a standard water softener(tank..salt..resin).  I mainly keep 
>live-bearers, and while they probably preferred the hard water from the 
>tap, they have not seemed to be too adversly affected by the soft water.

>So.... what might I expect by adding CO2 to water treated with the 
>water-softener?

Let's look at what you have in both cases.

Your tapwater has lots of dissolved Calcium Carbonate and Magnesium Carbonate
in it.  So there's Ca++ Mg++ and CO3-- ions floating around.

Now, the water softener replaces Ca++ and Mg++ ions with sodium (Na+) ions;
at least I think that's how it works (my parents' softener yeilds water with
an extremely high KH, but zero GH).  This is the same as if you dissolved a
whole lot of baking soda in your water.

CO2 injection messes with the CO3-- ions, so I would theorize you will get
the same results as everyone else's CO2 injection.  Cool! It should work. 

HOWEVER, as you point out, the livebearers may be happier with the hard tap
water, since that is closer to their natural surroundings.  Some fish are
not really happy with too many sodium ions in their water (which, I suppose,
is why using straight baking soda is not a good idea?).
Maybe you could experiment with different concentrations of both tap and
softened water.

I would like to hear some experienced sci.aquaria.chemists impressions on this,
as it's relevant to some of the Chemistry FAQ that we're revamping.

       - Erik
--
---
Erik D. Olson                		The Job-o-meter:
(e-mail)             	stand by...



CO2, Ph, and water-softener

by ac554-at-FreeNet.Carleton.CA (David Whittaker)
Date: Wed, 5 Apr 1995
Newsgroup: rec.aquaria


In a previous posting, Erik Olson ((e-mail)) writes:
> ac554-at-FreeNet.Carleton.CA (David Whittaker) writes:
> 
>>Suppose you add an overflow pipe to the tank. And suppose you allow a
>>pH meter to control a solenoid attached to the outlet from a hydrogen
>>zeolite water softener. This lets you add CO2, lower and determine
>>the pH, and reduce much of the hardness without adding Na+ ions. There
>>are no high pressure cannisters, no CO2 reactors, and no needle valves
>>to worry about. The resin is probably expensive, but this might be a
>>solution if one has a smaller tank. Comments?
> 
> Could you explain briefly how a Hydrogen zeolite water softener works?
> How does it add CO2 to the water?  I'm very curious now.
> 
>       - Erik

Instead of exchanging Na+ ions for the cations in solution, the
resin substitutes H+ ions. The carbonates become carbonic acid,
the sulphates, sulphuric acid etc. The harder the raw water, the
lower the pH of the effluent. It is used in industrial processes.
The softener would have to be connected to an open water line
and a method would have to be found to treat for chlorine/chloramine.
The equations I'll leave to someone more learned. I'd be curious
to know if such an approach is feasible.
--
 


CO2, Ph, and water-softener

by gqva06-at-udcf.gla.ac.uk (Wilson Angerson)
Date: Fri, 7 Apr 1995
Newsgroup: rec.aquaria

In <D6K4JK.7sK-at-freenet.carleton.ca> ac554-at-FreeNet.Carleton.CA (David Whittaker) writes:


>In a previous posting, Erik Olson ((e-mail)) writes:
>> ac554-at-FreeNet.Carleton.CA (David Whittaker) writes:
>> 
>>>Suppose you add an overflow pipe to the tank. And suppose you allow a
>>>pH meter to control a solenoid attached to the outlet from a hydrogen
>>>zeolite water softener. This lets you add CO2, lower and determine
>>>the pH, and reduce much of the hardness without adding Na+ ions. There
>>>are no high pressure cannisters, no CO2 reactors, and no needle valves
>>>to worry about. The resin is probably expensive, but this might be a
>>>solution if one has a smaller tank. Comments?
>> 
>> Could you explain briefly how a Hydrogen zeolite water softener works?
>> How does it add CO2 to the water?  I'm very curious now.
>> 
>>       - Erik

>Instead of exchanging Na+ ions for the cations in solution, the
>resin substitutes H+ ions. The carbonates become carbonic acid,
>the sulphates, sulphuric acid etc. The harder the raw water, the
>lower the pH of the effluent. It is used in industrial processes.
>The softener would have to be connected to an open water line
>and a method would have to be found to treat for chlorine/chloramine.
>The equations I'll leave to someone more learned. I'd be curious
>to know if such an approach is feasible.
>--
> 

It won't work unless you can find a way of maintaining a stable KH. In
the form you describe it, KH will be demolished in short order because
you will be continuously adding acidic water to the tank. Take a look at
it quantitatively:

Suppose the water has a KH of 20 dKH (about 7 meq/l) before passing
through the softener, to take an arbitrary but high number. Assuming
that this is all in the form of bicarbonate, after cation exchange you
have 7 mM carbonic acid in the softened water. In more familiar units
that's about 300 ppm CO2. pH will be 4.2 or less.

Now look at how much of this water you need to add per day to maintain
an appropriate concentration of CO2 in your tank. George Booth's CO2
loss experiments in a 90 gal tank suggested a CO2 loss to atmosphere
under best-case conditions of about 2 ppm per hour when the
concentration was 15 ppm. Several factors could increase the overall
rate of CO2 utilisation under real-life conditions (e.g. plants, smaller
tank), but let's stick with 2 ppm per hour or 50 ppm per day as the rate
at which you need to replenish CO2 in the tank. (That would translate
into about 1 lb CO2 per month for 75 gals of tank water, which I think
is not unrealistic). That implies that you need to replace approximately
50/(300-15) = 18% of your tank water per day with the CO2-enriched softened
water just to supply enough CO2. Maybe you could reduce CO2 loss
somewhat, but you are still looking at replacing a substantial fraction
of tank water each day.

Even if you could rig up some kind of automatic overflow and drain,
adding this much water is going to destroy your alkalinity/KH at a rate
of over 20% a day through dilution alone, and possibly much more
depending on the pH of the softened water. Using a pH meter to control
CO2 injection requires a stable KH, and it works for gas injection
because KH normally declines very slowly. At a contant pH, CO2
concentration is proportional to KH, and you would end up with both CO2
and KH on a rapidly falling exponential curve. It would be possible in
principle to compensate for the loss of KH, but it's no trivial matter.

Personally, I think I'll just stick to my trusty conventional CO2 setup :-)

Wilson






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