I would go for a very fine pebble gravel it cuts down on the scratches and it doesnt stck to the rays disk this is not so much of a problem with brown rays like motoro/pearl but it does piss me off with black rays
another idear i have been planning for my next tank is to cover the base of the tank with silacon and spreading a fine layer of gravel over the tank base before you fill the tank this way you wont have the bare bites of tank were the rays keep pushing the gravel around
another idear i have been planning for my next tank is to cover the base of the tank with silacon and spreading a fine layer of gravel over the tank base before you fill the tank this way you wont have the bare bites of tank were the rays keep pushing the gravel around