Tank 4 is the hardest tank in all of Insaniquarium. Guppies are harder to get. Prices have increased dramatically. Do you have what it takes to finish this tank?
Tank 4-5 - Cyrax The Evil Alien Mastermind is the leader of the aliens who have been attacking your aquarium. He's not really a pet, but he is what you get after beating the level. Price: $299997
Bilaterus - an alien with two heads. Both heads must be defeated to truly defeat Bilaterus.
Ultravore - a large fish who drops Treasure Chests. Each treasure chest gives the player $2000. The ultravore is pretty much the key to finish Tank 4, though due to its large size, it is the most vulnerable to aliens. Price: $10000