Originally Posted by Fishybusiness
Thanks guys. Would adding sand to a portion of the tank work or would we have to change the entire thing?
This is possible, but substrates will mix together over time unless they are well separated in a permanent manner.
When I was preparing to change the substrate in my 5-foot tank from fine gravel to sand 2 years ago, I considered something like this. I thought a deeper enriched substrate along the back (for the large sword plants) sloping down to a nice sand streambed along the front would be ideal to create an Amazonian riverbank setup. But the problem was keeping the two divided, and the only way to do this is with a barrier of some sort that is siliconed to the tank bottom glass and the side walls. There is a continual flow of water down through the substrate, and this plus the force of gravity will level out and mix the substrate. In my sand and gravel tanks, the nice terracing effect I create with heavy chunks of rock initially look wonderful, but within a few months the sand or gravel behind the rocks is lower and the front is higher.
I end up with an even substrate regardless.