what type of piranha are you going to keep. if you are going to keep a rhombeus than yes as long as it is small. it will only be suitable till it gets 5 to 6 inch than you will have to upgrade to a larger tank. if your going to keep red bellied piranha it will only be suitable for a small group of juvenile piranha only for a short amount of time because they grow really fast. i've kept 9 5inch red bellied piranha in a100 gal tank. and right now i have 5 juvenile black peru rhombeus in a 100 gal no fighting as long as you pute wood and plants and make sure that they are full all the time that way they don't try to kill each other or nip fins. good luck