Ingredients:
1. A whole fish. I bought a 550 gram siakap (barramundi) from a hypermarket for RM4.95. Scaled and gutted too on the spot.
2. Coarse salt. I used about 1 KG of it (3 x 350 gram).
3. 4 tbsp of water (add it to the salt and mix well)
Oven: 200 deg C for 20 minutes. My oven is the bowl type Halogen Convection Oven
A 550g siakap, gutted and scaled.

You don't have to use foil here. I used it only because I do not have a baking tray. Make sure you put a layer of salt on the tray before laying the fish on it, then cover the whole fish with salt.

Check the youtube clips I embedded below. Some prefer to leave the head and tail uncovered.
200 deg C for 20 minutes. This is what it looks like after 20 minutes.

Use a pastry brush to get rid of as much salt as possible from the fish.
This is my fish with all the salt crust removed.

Remove the skin.

Slightly overbaked in this case but still very tender and succulent. I think I will reduce the baking time to maybe 17 minutes.

Check out the following clips and you'll notice some of them prefer to use salt and eggwhite and/or flour to form the crust. Some even add spices/herbs to the salt & eggwhite mix.