The cap on the soil will keep the soil from becoming soup in your tank, will also keep fish from rooting around in it and making a mud tank 
I had my last tank set up with plain ole dirt and the small natural color gravel on top, it grew beautiful plants. But when I decided to tear it down oooo what a mess lol. I liked it, but I wont do it again at least not on a big tank. OH and I had a couple of inches of dirt in mine and for lighting I just used shop lights.
I had my last tank set up with plain ole dirt and the small natural color gravel on top, it grew beautiful plants. But when I decided to tear it down oooo what a mess lol. I liked it, but I wont do it again at least not on a big tank. OH and I had a couple of inches of dirt in mine and for lighting I just used shop lights.
