As a relatively new Cory owner, like you i had rounded gravel in the tank but after a few days i decided it wasnt right for my Cory's. So i took the fish out and scooped out all the gravel with a dust pan, which took 2 minutes, then put in my pre washed fine silica sand which is about an inch deep. It was the best choice i made before the aquarium got established fully. The Corys love digging under the bogwood and the base of the tank never stays the same longer than 24 hours. Had i stuck with the rounded gravel, there would be no self dug hiding places. Also the gravel is a lot harder to clean requiring a more forceful hand, with the sand you can just skim over the top easily sucking out all the mess. Reconsider sand as an option and you wont be disapointed and neither will your fishies