well 1st i got a leporinus that wont eat. hes in a 15 gallon tank alone cause he triued to kill anything near him. hes only 3" now. i looked him up online and it looks like the stupid girl who sold it to me saying, yea hell be ok in ur tank(15 gallon) even though apparrently they get to be a frickin 1' long and are known terrorists of the aquatic world. he usually eats guppies, tetras and goldfish ( goldfish he harrasses without end until they tire out in a corner where he nibbles them to death, sorta like the dinosausrs did in jurassic park LOL). anyway, he just stopped eating all of a sudden! i have no filter in the tank, just an air stone and big ( largest one i could get - like the Hydro 8 or soemthing made for 110 gallon tanks!) sponge filter with weekly 30-50% water changes due to his eating habits...anyway, plz help and advise.