What kind of fish do you have in the 75?
I would remove the coral rock. My personal opinion is that, those fake coral decorations really don't have a place in the freshwater hobby because there are no reefs in freshwater. No coral will ever be able to survive in freshwater. But again the aquarium hobby is a way for fish keepers to create a drawing with the fish tank being the platform and the fish and decor being the masterpiece.
Anyways, way off point, I second the idea of driftwood. Driftwood will make your tank look very natural. You can also go outside and pick up some rocks bring them in and boil them. You can get them from your yard, pond, etc. Just make sure they don't have any sort of chemicals or are man made rocks.