2 months? I dont even think 2 months is long enough to wait for a tang. I would give it more like 4 months for the tank to mature. You need to establish excellent water parameters and a good bacterial bed. 5 fish is more than you should put in a 3 week old tank. After 3 weeks the tank probably isnt even finished totaly cycling yet. Space the addition of new fish out more too. You should wait like a month after your first fish, then 3 weeks after second fish, 2 weeks after third, and then a week after each additional. Always watch the water parameters too. You also have to remember with 5 fish in a 75 gallon you are approaching your maximum, that is if you havent already reached it yet. 1 inch of fish for every 5 gallons of water. That means 15 inches of fish. I wouldnt push it past 1 inch for every 2 gallons.