Hi, I have a 5ft by 2ft by 2ft tank, and im just wondering about how many fish would i be able to fit in it and what size heater would i need. i bought the tank of ebay and it came with a 300watt heater. At the moment its holding a arrowana, 6 angel fish, 2 small oscars, 2 small birchirs, 1 small fire eel, 3 gurramis, 2 jack dempseys, 2 rainbow fish, 2 plecs, a featherfin cat fish and 2 small barbs. Is this too much?, i am using a 600 ltr external pump for the tank.