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Re: No CO2

>>  Actually, I know
>> that CO2, or carbon, is essential to plant life.  It's just that I prefer
>> more natural and simpler ways to get it, like from fish food and decaying
>> organic matter.

Yes, carbon is important. It makes up ~45% of plants. However, CO2
--whether is be from from fish food, decaying OM, or from a pressurized CO2
cylinder -- is NOT the only way to provide carbon to plants. While there
are some underwater plants that do depend on CO2 as their source of carbon
(including Echinodorus tenellus, Riccia, Ceratopteris, Ludwigia repens),
many other submerged plants are able to used bicarbonate!! The ones
published in the literature include Egeria densa, Elodea canadensis,
Potamogeton sp. and Vallisneria sp. These are plants whose native habitat
includes hard water (i.e. with high HCO3- concentrations). There are others
which are found in hard water: Cryptocoryne affinis, C. aponogetifolia,
Bacopa monnieri, Sagittaria subulata, .... and others which also have this
capability, but you may see deposits of calcium on their leaves.)  

You can have a very lush plant tank using these bicarb users - without
added CO2 - but you may have to do water changes, have calcarious materials
in the tank, or add chemicals to keep the KH up.

Even for the CO2 dependent plants, you can have a nice tank if you can get
the CO2 from the substrate. I had a 70gallon low KH, non-CO2 injected tank
going for over 5 years with wall to wall chainswords and a variety of other
plants. It had a substrate whose lower layer was 50% peat and 50% coarse
sand. Eventually, the substrate stopped providing sufficient CO2 and lush
plant growth declines. I revived the tank and since kept it going with
injected CO2 from a pressurized tank.