My brother brought home a small (around 1-2 inch.) goldfish from a carnival. I have a 30g tank with 3 Albino Cory Catfish, a female Betta, a Marineland Penguin 150, and a Steal-Pro heater set at 78 degrees F. Can I safely add the goldfish to this set-up? I realize that goldfish need much, much larger tanks and do not require heaters, but this is my only option besides let him put it in a .5 gallon bowl.