A Simple Way to Organize Your Dosing Lines The IceCap magnetic tube holder universally mounts tubing securely to most smooth locations up to 1/2in thick. Also available as a 4-Tube holder and a 4-Probe holder. Magnetic holder can be fixed on the sump or aquarium wall and can hold up to 2 dosing tubes. Dimensions (LxWxH): 2.875 x 2 x 1.75in