Piranha will essentially bother everything you put in the tank. It's just their nature.
A ropefish, besides most other aggressive fish (which the rope isn't) is neither bigger nor more aggressive than the piranha and it will find it an easy prey item.
Unfortunately, with piranha, you're resigned to a species only tank
Also, what you mean about a fish growing to its enviroment... thats only partly true. A fish in a 300gal tank can grow larger than one in a 120 if it is destined to do so, but a fish that WILL grow so long as 3" will be by no means stunted completely if put in such a small tank, and even if it could - it would not be healthy to have done so. (Not critizism at all, just letting you know.)
A ropefish, besides most other aggressive fish (which the rope isn't) is neither bigger nor more aggressive than the piranha and it will find it an easy prey item.
Unfortunately, with piranha, you're resigned to a species only tank
Also, what you mean about a fish growing to its enviroment... thats only partly true. A fish in a 300gal tank can grow larger than one in a 120 if it is destined to do so, but a fish that WILL grow so long as 3" will be by no means stunted completely if put in such a small tank, and even if it could - it would not be healthy to have done so. (Not critizism at all, just letting you know.)