My favorite schooling fish are rummynose tetras. Regarding your current stocking, iridescent sharks are actually catfish which get very large and are food fish in Asia. They are also very jumpy and usually injure themselves against the glass when spooked. Definitively a fish which shouldn't be offered for sale. If your pleco is a common pleco, as opposed to a bristlenose pleco, it too will grow too large for the tank. They are also pooping machines. I would rehome the pleco and shark.