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Re: CO2 with hard water?

>Date: Thu, 21 Aug 1997 10:46:51 -0500
>From: John Pitney <pitney at uiuc_edu>
>I am setting up my first planted tank (a 55), and after reading 
>everything I can find on the subject, I have decided that I'd like 
>to buy a manual "welding shop" CO2 system.  Here in Champaign, 
>Illinois, the tap water is really hard (according to the local fish 

Test it yourself.  Don't trust what they tell you. If they have not dealt
with CO2 injection, their terms for "hardness" may not apply to what you
want to do. 

Get a Tetra Hardness test kit with KH and GH tests.  The GH value is what
is used by most aquarium books when they say a fish or plant likes hard or
soft water.  GH is the measure of calcium and magnesium in the water and
does NOT
affect pH.  The KH value refers to the amount of buffering in the water and
DOES affect pH.  

>As a practical matter, will it be difficult to dissolve enough CO2
>in my tank to get good plant growth?

Water hardness (the KH value) doesn't really affect how much CO2 you can
dissolve in the water. IMHO, you can get an ideal 15 mg/l of CO2 into any
water fish can live in. 

>According to the chart, it looks like the CO2 concentration will be
>really large if I get the pH down to 6.8 or 7.0.  

The chart is based solely on KH hardness.  You have not indicated what the
KH value is, so you really can't state what the CO2 concentration would be.  

We *boost* KH in our tanks to 5 dKH (about 90 ppm of bicarbonates).  This
gives us a pH value of about 7.8 with equilibrium levels of CO2 (2-3 mg/l).
 When we inject 15 mg/l of CO2, our pH is around 7.0.  So your water may be
perfect for CO2 injection.  

Get a Tetra hardness test kit (they're cheap) and find out for yourself.
"Trust no one" at a fish shop. 

>I want to have
>healthy S. American fish as well as healthy plants, so should I shoot
>for the optimal pH--6.5 to 7.0 and stable--or should I shoot for
>the optimal CO2 concentration--10 to 20 ppm--which leaves the pH
>somewhat high?

Unless you're breeding the fish, they can adapt to almost any water.  If
they are captive bred, the "natural" pH values may be irrelevant anyway --
put them in water they are used to.  A pH of 7 with 15 mg/l of CO2 and 5
dKH should support most fish.  Adjust GH to suit the biological needs of
the inhabitants.  

>Even if I can inject enough CO2, is the hardness of my water in itself
>going to be a problem for (some?) plants?

Wait until you find out what the hardness is before you get too worried. 

>Are there any plants that are known to do well or to do poorly in
>CO2-injected hard water?

Most plants do well, few do poorly.  Some may grow too fast and get
"stringy" but that is a subjective aesthetic factor, not a "doing poorly"

George Booth, Ft. Collins, Colorado (booth at frii_com)
Need info? http://www.frii.com/~booth/AquaticConcepts.htm