Bring a large pot of salted water to a boil, add the macaroni and let it cook until al dente; drain well.
In a medium-size mixing bowl, combine onion, bell pepper, celery, mayonnaise, sweet pickle relish, ketchup, pickle juices, horseradish, hot pepper sauce, parsley, celery seed, chili powder, salt, black pepper and shrimp. Fold the macaroni into the mixture. Cover and chill at least 3 hours before serving.
