CorallineAlgae
Aquarium Advice Addict
I don't think most people mix all of this stuff together. Generally, the most plant nutritious substrate goes at the bottom. This layer is often "capped" by another layer that is chosen for a certain benefit: easy to plant in, soft for catfish, gives the tank the look you're gunning for, or another reason... I'd say maybe put the Eco Complete as your bottom growth layer and cap it with either Flourite or your gravel. Both should be easy to plant in. Other than that, I wouldn't know how to advise you. Honestly, if you just want to mix them all up I don't know a reason not to give it a go. Plants can grow in nearly any substrate.