Its always a gamble. I had a stellatus and stars and stars and stripes puffers in a 300. They grew up together. They were both around the 15" mark when they fought it out to the death one night. No obvious reason, they just decided to duke it out. I lost them both. I had a map puffer that would kill just about everything and would even cut the cords off the power heads. They might be fine one day and not the next. Just keep a close eye for agression if you do keep more than one.