Fantail Fish

Question
Hi,
I recently bought a fish tank, 2.5, for my bro's birthday and it bought 2 fantail
goldfish. I want to knw when will they fully be grown? What should i feed them
besides flakes and what other fish are compatible with these fish.
Thank You ^^,

Answer
I hate to break this to you, but your fish will be dead in a matter of days or weeks.  A single fantail needs 10-15 gallons of water each...two will not survive in a 2.5 gallon tank.  They grow quickly, but cannot grow when crowded into too small of a tank.  Their insides keep growing while thier bodies stay the same.  Eventually there is too much internal damage and they die.  i would suggest taking these two fish back and buying a nice pretty betta fish.  The betta is the only fish that can be happy in a 2.5 gallon tank.  I'm sorry to be the bearer of bad news