Carbon dioxide is one of the other major factors that will decide whether the plants grow to there full potential. There are currently a few ways to deliver this to the plants, some are easier and some are cheaper but they all do they same thing.
Buying a pressurized bottle and having a solenoid valve is by far the easiest and best option, they only problem is price. The regulator will allow you to exactly tune the CO2 output to give you the best results and unlike DIY it will not leave a residue on your diffuser
DIY CO2
This will do the same thing as pressurized but is more of a hassle and needs to be changed every few weeks. It will not work through a diffuser, but injecting it straight into the filter or into an up turned cup will work just fine. The upside, it is incredibly cheap.
CO2 Liquids
Seachem Excel and other forms of carbon in a liquid work fine. This is not really a cost effective method though, and it may be a hassle to continue using the product every day or 2nd day.
CO2 tabs
I have never tried these, but i don’t think they are at all effective and will only work for very small tanks, best to avoid these.
Electronic CO2
The electronically generated CO2 is also said to work ok, but once again only for smaller tanks, and the refills are considered slightly costly.
Choose carefully, but for the long term, if you truly believe you have a passion for aquariums and you have money to spend, buy the pressurized CO2.