Challenge Mode is the hardest Mode you could play in Insaniquarium, because every time an alien comes into the tank, the next time there will be twice as many! Plus, all prices will grow over time. Every time you buy an egg piece, all prices exept the egg piece will reset. If you win, you get thousands of shells!!! Tank 1 - 2,000, Tank 2 - 5,000, Tank 3 - 10,000 and Tank 4 - A whopping 20,000 shells!!!!