So I am thinking of getting some ADA aqua soil. I have a 55 gallon tank. Standard dimensions 48x12 (i think). I want the amazonia because it is the darkest color. How many liters would i need for 2-3 inches of depth? Should i get anything to go below the substrate? Like their power sand??? If i do get that how much would i need? This stuff is so damn expensive!!!!!!!!