He has at least 6 fish that should get close to or over 12". Think of 6 fish almost or over a foot long, swimming around a 6 foot tank.I have a lot more fish in my 180 - almost 3x more LOL! - but only a few larger fish. Also mine has a lot more rock in it, with additional rock in a large sump. Your aquascape doesn't provide much room for fish to hide.
What is "MI" ?
I would look online and do some research on aquascape and try to copy that. Can't really tell you to buy X amount of rocks, as some are large but light, some are small but heavy.Makes total sense! I think I'll start by adding more rock. My fear was to overcrowd them with rock. How much more would you suggest?