The amount of rock you have is fine, however the kind of rock you have is big and solid. The big pieces of rock make great base pieces but you may want to consider replacing those boulder like rocks sitting on top of the base rock with some lava rock or a different kind of rock that has more pores and more little nooks for them to swim around. Fish like to have sections of rock to swim around and hide in when they are scared and or at night. I played around a ton with my rocks and still do almost every-time I clean and do a water change. You can almost never have TOO much rock fyi. The only danger is adding a TON of new rock to a new tank causing it to re-cycle and potentially poisoning your tank in the process.