Thanks for the ideas, will give that a try, its not much thinner than an airline tube so would probably do it. if not i can always use the airline clips to hold the airline for the co2 in place. if i cant get it to work or can't get hold of any then will have to go with the tape and substrate idea and hope i don't mess it up when plantingdepending on its diameter you may be able to use the air line suction cups they sell in Pets at Home. Its 6 cups for about £3 - might work might not (can you tell I have my intelligent head on tonight )