so my brother upgraded from a 30 gallon to a 40 gallon 2 weeks ago. i took his 30 gallon and made it into a freshwater tank about an hour ago, while his is salt water. right now i dont have any plants, rocks, anything.....just gravel and 4 dumbass fish. what should i buy to make this thing awesome? i remember someone had a clown knife or something, that would grow huge and kill everything and such, but would that work in a 30 gallon tank and on a limited payroll (i have no job and about $300). what should I do?