Carbon and Aquatic Plants

So here is a bit of science about carbon and aquatic plants:

The carbon used by aquatic plants is in the form of ‘Dissolved Inorganic Carbon’ (DIC). In freshwater DIC comes from 4 sources; CO2 (carbon dioxide), H2CO3 (carbonic acid), (HCO3)2 (bicarbonate) and CO3 (carbonate). At air equilibrium, the concentration of CO2 in water is about 0.5mg L. CO2 diffuses into plants about 10,000 times slower in water than in air. Therefore, aquatic plants need about 30mg L free CO2 to reach full saturation of photosynthesis. CO2 demand shares a direct relationship with light intensity ie. At low light intensity light is a limiting factor and at high light intensity CO2 is a limiting factor. 

So how do I get more CO2 in my planted aquarium?

CO2 injection or liquid carbon source. CO2 injection comes from a cylinder through silicone tubing and is forced through a very fine diffuser – producing minute bubbles. Liquid carbon sources like Easy Carbo by Easy Life is less effective than injection but can be useful when injection isn't a practical option.

Maintaining CO2

Agitation of water surface and aeration will disperse CO2 down its concentration gradient – ‘loosing’ it out of the water into the air. The only time aeration should be encourages in a well planted tank is when fish and plants are using it (at night) – and only if fish start gasping.