You can buy these in places like petsmart and petco, believe it or not. Flourite is sold in Petsmart, Eco-complete in Petco. If you buy the Eco-Complete online- its on sale for only $16 for 20lbs and is only $6 to ship! Holy coockaracha.
Each one has their own issues, pros, cons...
Flourite kicks up a TON of dust and requires lots of rinsing, a few hours, even.
Eco-Complete has less kick-up, but comes in many less colors.
ADA Aquasoil tends to be much more expensive, and some say less effective. (open for debate)
I second the fertilizer note- but be warned: plants like anacharis, mosses and a few other plants have been known to melt when using Flourish excel.
Thanks for the reference, Nex :D <3