The fish that you are talking about with "the big brain" is an oranda. I agree with the above post you need at least a 100 litres for those fish as goldies grow quite large and they need a lot of fitration as they are poop machines. If you are having trouble paying for a larger tank join up to freecycle and put an advert on asking for a tank you would be suprised at the response and it won't cost you a penny.