I know about the pros and cons of gravel but what about sand?

Sand isn't recommended for a goldfish tank. Goldfish root through the substrate looking for food and the sand can irritate their gills as they root around. Sand also gets sucked up by the siphon when you're vacuuming your tank. Sand also compacts and can become anaerobic, which can release hydrogen sulfide gas into the water either harming or killing your fish... Stay away from sand in a goldfish tank.