For Acrylic Tanks: Acrylic-safe Replacement Pad Kits All Algae Free aquarium cleaning magnets must use acrylic-safe scrubbing pads when cleaning acrylic aquariums. Each kit includes:rn (1) Adhesive-backed natural felt pad for protection on outer surfaces of acrylic tanks (3) 9″ x 5″ acrylic-safe inner scrubbing pads (makes 12 Hammerhead Float pads) (1) Self-adhesive, non-toxic medical grade Velcro pad for holding acrylic safe scrubbing pads on inner assembly