pea gravel

I'm creating a self sustaining aquarium. Well, have been for about 7 months now. The tank is roughly 20 Gallons, I have a ~2 in level of sand/kitty litter, with a ~1 1/2 in level of Pea gravel on top of it. I have Amazon Grass planted, Java Moss, and what I can only think is Anubis planted in...