
Your gonna struggle fixing it under water. These things are nothing but big sheets of polystyrene. Really you need to empty the tank dry it properly, empty the substrate, silicone the backing on, wait 24 hours to let it dry properly. I asked the same question as you before attatching my juwel backing.

Well if you want to do it that way its not so bad. You can buy a big plastic tub (which are always handy anyway) from a DIY store they are not expensive and put everything in that and run it for a day or so while you stick your background on.Just think of it as a good oportunity to give your tank a thorough clean!![]()