Hi guys. Im going to be setting up a 75gallon in about 2 or 3 weeks. Im planning on using a canister and a HOB with some live plants. The stock is 1 BP (currently have) 10-15 tetras (congos OR black skirts), and 6 cory cats. I was planning on using gravel, but would sand be better for the cory cats? Or is gravel ok for them?