I agree it's a cool rock! In my amateur opinion, it's probably fine, as long as you're vigilant about your levels and water quality, since it looks like you have a pretty light bio load. However, your fish might be happier with a little more open space for swimming. I'd switch it out for some smaller rocks, and save the big one for a bigger aquarium. Some living plants would also be great for the tank, for the look, for health, and for giving your fishies lots of hiding places.