Thanks souffle for that idea! I`ve heard people say they use velcro to hang bottles, but I suppose I was looking for something a bit tidier looking! A permenant metal or plastic device that I could slip the metal hook of a bottle hanger through. I take the velcro idea on board though and if this is the only solution to me, then I`ll go for that.
I`ve also taken out the small wire ladders and replaced these with a long critter-trail tube that runs down from the shelf to the floor, as I feel robos might prefer this tunnel system of getting to the level above, rather than trying to climb ladders. I feel they are not great ladder climbers!
I`m only using this tank for perhaps a single robo rescue that might become available at some time. I normally use larger glass aquariums and/or Duna plastic style housing. But I won this tank for £10.50p so it was a bargain!