Re: Re: [RML] Planted Tanks

Nick Thorne (nick at
Wed, 6 Aug 1997 09:44:15 +1000

G'day all,

Harro Hieronimus wrote:

> Don't forget that plant nutrition and plant growth does not depend
> from CO2 or iron or phosphate or
> light or .... but from a sufficient mix of all. If you blow air into
> the water by a filter or a membraneous
> pump, you also add CO2.

Umm... I'm not sure this is correct. CO2 is not very soluble in water
and the gas exchange at the surface favours the transfer of CO2 to the
atmosphere. Blowing air into the water increases gas exchange by
disturbing the surface layer and so CO2 levels are consistently lower
in tanks with air, or with filters that rapidly circulate the water. I
have monitored CO2 levels in aquaria and found that if the stocking
rate is kept low so that O2 requirements do not become excessive (thus
requiring air or other measures to keep the O2 level up), then using a
canister filter set up so as to break the surface tension, but not too
dramatically stir up the water, adequate CO2 levels were attained.
However, in tanks with air driven filters or air stones, there was
always less than the desirable amount of CO2 for plant growth. The
only way to resolve this issue, AFAIK is to use CO2 injection. An
expensive option, better IMO to keep the stocking rate down and avoid
air wherever possible.

BTW, when keeping larger fish in aquarium as NFA does in our trout cod
hatchery (our biggest trout cod is around 5 Kg), plant growth is not an
issue. We use bare tanks with sub-gravel filters in large ice-cream
containers. We also use air stones. Most tanks have two of each. Our
main problem is O2. Of course, this is a high maintenance environment
and a lot of effort goes into looking after our fish. If the
temperature is high, we would have a problem if we lose air and our
water quality is not 100%. Naturally we expend a great deal of effort
to ensure that neither condition happens.



Nick Thorne nick at

Native Fish Australia