Note: Unicel Part# was formerly c-5303 replacement for: Marquis Spas 20041 (note: new design. Unicel Part# was formally c-5303); Unicel 50 Sq. Ft. Top load (note: replacement for Marquis Spas. Unicel Part# was formerly C-5303); Marquis Spas 370-0237 (note: new design. Unicel Part# was formally C-5303); Cal Spas