Personally layering substrate is a pain in the ass, it just all gets mixed up in the end. From personal experience... I have a 55g densly planted tank and i use aquariumplants.com's substrate. Its about 1.2-2.8mm so its a small grain so it wouldnt be the greastest to use with larger fish but it still does a good job. It comes in 3 colors and it has minerals in it that help with plant growth. Its reasonably priced too. Thats what i use and my plants thrive in it. I was gonna layer substrate too when i started but its just not worth it, it gets mixed up anyways. I bought a 5 gallon pail for my 55 and its plenty. The plant anchors they have work very nicely too in the substrate. It doesnt break down at all either.