I plan on having a plants in my tank and read it is good to put soil in for the plants. I want to put maybe an inch of organic soil under a black sand cap. I was wondering how big the sand cap should be and what type of soil is recommended? I read for the black sand and a good brand is Estes also known as Stoney River. Additionally I have a 29 gallon and wonder for 5lb bags, how many should I get?