After the second story mission, where you follow Marlin in a 3D environment for the first time, you'll be tasked to clear an area of some old shells.
This will then allow you to build the
Morro Bay Store (1/5). As soon as you've built it, you'll be able to shop in it, but the other buildings aren't for sale yet. You'll have to keep collecting shells in the story levels, so go to the objective.
After doing the first level after building the store, I managed to find 17 of the 20 lost fish, and got 2 of the sand dollars, thanks to using the shrimp you get at the end of the level to clean algae throughout the instead of using the exit pipe straight away.
We can now use the shrimp in Morro Bay to clean the algae around. There will be three patches of algae for the shrimp to clean. We can now buy the
Brain Coral Fish Changer (2/5). We're only allowed to place one, so do so, then go back to Marlin.
He'll tell you to "Brighten the place up a bit". Decorate the objective, and you'll unlock a challenge. Ignore that for now, we can do it later. Go to the new objective for the next level.
Complete this level, and then the following level will be another fish-collecting level. Get to the end of this level, beat the boss, and you will be able to get the cuttlefish, which will now be on your
.
You'll now go back to Morro Bay. There will be a mission from a large seahorse where you have to collect three seahorses from around the area, so do that. There will also be a mission to rescue three fish trapped in algae. So do that too. There is another mission regarding the Brain Coral Fish Changer, but we can't do that yet. Go and see Marlin. He will give us a task to do with the cuttlefish.
The cuttlefish will lead us to the 'Shrimp's Diving Helmet' item behind the light-sensitive water plants. Go back to Marlin, and set it up as a building.
Shrimp's Diving Helmet (3/5).
Marlin then insinuates we should repeat some previous levels to get fish that we couldn't get in the levels we've played before, but we aren't going to do that yet, because we still need to upgrade our cuttlefish. The shrimp can now also eat through red algae, which will help us as well!
We can now also buy the
Coral Pipe Organ (4/5) Building from the Marro Bay Store, so do so, and place it.
We can't do anything else now, so go to the mission objective marker. Play the next unplayed level. This level will have a lot of red algae in it.
Remember, you can only go through red algae through the side that has green algae on. I.e. the red algae can only be cleaned in one direction. Finish this level, and then two more after that.
After completing that third level, killing the Anglerfish Toy, and unlocking the Hermit crab (who is adorable, by the way), and the ability to purchase the 'Sonar Central', you'll be on the level select. You can either go to the next level, or go to Morro Bay. Go to Morro Bay, go to the store, and buy your newly-unlocked
Sonar Central (5/5) from the Morro Bay Store, place it, and unlock your achievement!