In a large stock pot, melt margarine over medium high heat. Cook and stir chopped onion until translucent, but not darkened. Carefully add 3 quarts of water, increase heat to high, and bring to a low boil. Once boiling, stir in diced haddock and potatoes. Reduce heat to medium, and cook at a low boil for 30 minutes, stirring frequently to prevent sticking. Remove pot from heat, and allow to cool until mildly warm.

Stir non-dairy creamer into cooled soup, slowly and thoroughly to avoid lumps from forming. Season to taste with salt. Cover and refrigerate 8 hours, or overnight, to develop flavors.

To serve, reheat on the stove or in the microwave. Adjust seasoning as needed with salt. Serve with soda crackers and sweet pickles.