Cut the cod loin into 4 chunks that are similar in size to the buns. Salt the fish. Bring oil to 350°F in a Dutch oven or countertop fryer. Whisk the curry paste into a small amount of the water, then add the rest of the water and ice cubes. Add in the flour, corn starch, and salt, and lightly mix. Don't over mix, there will still be some clumps. The mixture should be thinner than pancake batter.