yeah it was a complete rebuild, took the plants and fish out - removed the old sand, had about 1cm of water in the tank only cause i couldnt get it out, put in the daltons, then a nice big thick layer of gravel, and replanted. i kept about 60L of water and put that back in before topping up and putting the fish back in.
i would have thought that keeping the water would have been ok but maybe its not ?