Happy Aquarium Cheats :
NoT cheat but still useful!
go to the store. then click decor. then click corals and then click next, to you see the "pink birdsnests coral" . It will cost around 1 pearl! buy it. then when you have bought it , press "sell" and you can get around 56 coins for each you buy! I got at least 300 coins for doing this because I bought 5 of them.