CO2, Calcium and Concrete

---------- Forwarded message ----------
From: "/PN=Steven.S.AMOR/OU=ENG4/O=SHELL AUSTRALIA/"@shell.otc.au
Date: 23 Dec 96 09:21:31 +1100
Subject: CO2, Calcium and concrete
To: Aquatic-Plants at actwin_com (Receipt Notification Requested)

Firstly, Merry Christmas to everyone!

I heard on my local radio station the other day that a few findings did come
out of that most famous Engineering failure - Biosphere II.

It seems that one of the reasons why they had to inject extra Oxygen into the
sphere was that the CO2 levels were way below expectation and so the plants
slowed down and stopped photosynthesising (sp?).  It turns out that when they
pulled the sphere down they found out that the concrete in the supports was
absorbing the CO2 and reacting with the calcium to form Calcium Carbonate. 
This is relevant to aquariums because I have never heard of this property of
concrete.  I don't have any concrete in my tank but one of my tanks does have a
few pieces of shells.  Would the CO2 react with the calcium is the shells?
Therefore, would it react with any calcium in the gravel? (Some people do use
crushed shells for substrate - particularly aquarium shops).

Are there any other substances that I should avoid putting in my aquarium that
will remove CO2?

Steve Amor,
Steven.S.Amor at Shell_otc.au

PS Could someone in US tell me what GFI stands for - In Australia we use an
"ELR" (Earth Leakage Relay) in the ONLY wire from Earth to Neutral to monitor
dangerous currents.