Preheat oven to 180°c. Line a baking tray with baking paper. Pour oil into a medium saucepan until 1/3 full and place over medium heat. When hot, add half the potato and cook for 12 minutes or until golden and crisp. Transfer to prepared tray and place in oven to keep warm. Cook remaining potato.
Meanwhile, place 1 cup of the flour into a bowl. Whisk in soda water until smooth. Place remaining flour into a shallow bowl. Lightly coat half of the fish strips with flour, then coat with batter. Carefully lower into hot oil and cook for 4-5 minutes or until golden and cooked through. Transfer to a plate lined with paper towel. Repeat with remaining fish. Season with sea salt flakes. Serve with tartare sauce and lemon wedges.