im not an expert in anyway... but i used eco complete in my 29gal tank.. i used a 20lb bag... i think the rule is 1lb of gravel per gallon of water. i shouldve used 1.5 bags but i didnt wanna buy a 2nd bag
eco-complete is hard.. its like black gravel. i did research on it long ago, and i forgot most of it, but to me its just black gravel soaked in ferts and nutrients.. (probably isnt)
at first it worked really well, but then i got clado algae from someone's plants.now i have a huge duckweed problem.. and it blocks all the light so my plants melted.
u can always add rootmedic tablets to your tank or dose liquid fertilizers if u wish.
i learned the hard way about mixing substrates and gravel.. its real easy to mix, real hard to separate =x