i am getting a 157 gallon 7 feet long by 2 feet wide my 18 inch tall i only have 3 reds biggest is 6 inchs i am thinking for getting more piranhas. first i can get 3 more 5 inch+ reds for $135. second i want to put some caribes in but i can only aford for 2 right now and they are only 4 inchs. i would like a diff kind of piranha in the tank but i only can get 2. what way should i go??