Tank 4 is the hardest tank in all of Insaniquarium. Guppies can't be bought directly, only brought up through mature Breeders, and fish like Carnivores return to hunt and be hunted by much larger fish. Only one new alien is introduced in this tank, Bilaterus. However, the diversity in returning aliens, as well as a dramatic increase in two-alien attacks can make a lot of work for a player.
Apart from other tanks, Tank 4 does not feature a bright dominant color for its aesthetic. Instead, it has a more dower, dark tone with a navy blue backdrop and tan to brown foreground objects. Besides the brown plants growing off of the rocks, the tank sets the mood as a very hazardous final stretch of the game, complete with a skeleton on the left side.
Inversely, despite the overall dreary feel, the theme of Treasure being in arms reach compliments the negative tone of the tank, with a large treasure chest overflowing with gold and golden objects to the right of the tank.
Cyrax is not a true pet, instead serving as the final boss in Tank 5, requiring the player to defend their pets against him and his alien swarm after completing 4-5.
|4-1||$9000||Introduction of Breeders.|
|4-2||$25000||Introduction of Ultravores. Bilaterus' first appearance|
|4-5||$99,999||After completion, leads into 5-1 instead of a Bonus Round.|
*Guppies cannot be bought in this tank, instead they are spawned from Breeders.
- Tank 4 is the only normal game tank which the player cannot directly purchase Guppies.
- It is also the only tank to begin without Guppies, instead starting with a Breeder.
- In Tank 4-4, as the first Destructor + Ulysses combo approaches, the alert ticker which would normally say, "Multiple Alien Signatures Detected" but it will instead say, "Fourteen Alien Signatures Detected" and after a few seconds switch to "Just kidding, only two!". That only happens once in the game, with further alerts stating "Multiple Alien Signatures Detected" as usual.
- It is a good idea to use Ultravores and some money collecting pets, since the prices of the egg pieces can be quite expensive in this tank, especially tank 4-5, where the egg pieces are $99999.
- $99999 is the highest price that can fit on the price tag. Anything over 6 digits cannot fit.
- It's good practice is to keep at least a maximum of three Breeders, as to not overwhelm yourself with guppies while preparing to get Carnivores.
- Alternatively, using a mass of Breeders alongside Amp can be a powerful strategy as well.
- Tank 4 is the only tank in adventure mode which does not introduce exactly 2 new aliens. While Tank 1 introduces Sylvester and Balrog, Tank 2 introduces Gus and Destructor, Tank 3 introduces Ulysses and Psychosquid, and Tank 5 introduces Cyrax and the mini-sylvesters, the only new alien in Tank 4 is Bilaterus.