This Silicone Airline Tubing is ozone resistant, and is very flexible and easy to use. Max psi of 30. It is easy to cut with standard scissors. It is 6mm in diameter, and is safe for fresh or saltwater.
Absolute Koi sell's this Silicone Air-Line Tubing in 1 meter increments, or by the roll. Remember it is always a good idea to have extra on hand.