my saes are slightly aggressive towards each other. the dominant and largest one will chase the others away from the cucumber i leave in the tank. they dont suck on any fish i have... and i have a lot of them ranging from an a quarter inch to 12 inches. then again, they dont really suck either, rather they nibble on things. they dont have a "sucker mouth". maybe the saes you have are very hungry or a more aggressive type than what we commonly see. either way i have no bba or staghorn algae, and they make an amazing schooling display.