Sounds like you are very new to the hobby. The rocks you are looking at are most likely meant to go into a filter and need a constant water flow over them to really do anything, they won't be beneficial as gravel. A jardini is not a fish for the beginner. You haven't stated what size tank he is in. This fish will require a 125gallons within a year and as a full grown adult it should be in a 180 gallon. I'm sure you paid a decent amount of money for the fish, It would be ashame for it to die because of your lack of knowledge. It will be up to you to decide what to do, but you would be best to have more experience before keeping a fish like this.