I'm using miracle gro organic potting mix in my tank and its great. It's a bit messy at first but with frequent changes it clears up. You want to do 1 part soil and 1 part gravel, maybe a little more gravel because over time the dirt rises up. Saturate the dirt on the bottom of the tank and pull in about a half an inch from the side. Then cover with gravel. Fill about two inches with water and start planting ( I waited till after the tank was done to plant because I didn't have plants at the time and it gets very messy this way, but it can be done). Then full with water, and do a full drain. Then refill again ( If its still a mess, repeat draining and refilling until it looks ok). It will leak tannins for a while but that is safe for fish and with normal water changes, turns out to be very efficient. Also a good idea would be to sift the dirt first to get some of the wood chips out, but they could be picked out by hand if you don't have a sifter.