the bioload determines how many fish you can fit in a tank, not how much of the bottom is covered, stingrays need heavy filtration and a huge amount of water changes, youd probably max the bioload before the bottom is covered, with stingrays you dont want it overcrowded, they require alot of room to maneuver and move around each other, and theyre not cheap so i dont even know why youd consider stuffing them into a tank like sardines in a can