I pretty sure even bamboo sharks need a min of around 300G+ to live comfortably for life...Great white shark and Manta Ray, haha jk, just any that would be in that category of species, i'll get.
So i would maybe say, before dismantling your tank and setting it up as a S/W tank for a shark or ray, you really look into whether or not you can actually house either of them for life before jumping into setting up the tank... may help you save a lot of money in the long run...