Mac Salad

Name: Mac Salad
Ingredients: 8 cups water; 8 ounces uncooked elbow macaroni; 3 tablespoons kosher salt, divided; 2 medium-size russet potatoes , peeled and cut into 1/2-inch cubes; 2 cups mayonnaise; 4 hard-boiled eggs , peeled and roughly chopped; 1 medium carrot , shredded on large holes of box grater (about 1/2 cup); 1 1/2 teaspoons garlic salt; 1 teaspoon black pepper , plus more for serving