Cook the macaroni, according to package directions, to al dente; then set aside and allow to cool.
In a large bowl, whisk together the mayo, lemon juice, fresh dill, dry mustard, garlic powder, celery seed, sea salt, and black pepper.
Stir the celery, scallions, and sweet pickle relish into the dressing.
Gently break up the tuna, and mix it into the dressing.
Fold in the cooled macaroni, and stir 'til it's fully coated.
Cover and refrigerate for 3-4 hours, or overnight, before serving.