Just thought of what must be one of the worst replacement exhibits at Colchester Zoo:
In around 2012, the Familiar Friends barn was renovated. While most of the Familiar Friends barn was home to domestic animals, it did include several displays for small mammals - in the year of its closing it was home to groups of tailless tenrecs and feathertail gliders (the latter the only ones of their kind in a UK zoo).
It was replaced by an indoor display for koi carp. Not only has it lost some interesting animals, but the exhibit doesn't seem to work well for the koi either. The tank floor is tiled, so the carp cannot grub around as they normally would, and over the years the tank has become increasingly stained with algae. Just about the only reason I go in there is to try and spot the Taiwan bitterling (which are, in all fairness, rather special - they are the only ones of their species in a European zoo), but I cannot help but think how much better it would have been had the building remained either for small mammals or taken on some of the rare birds from Raymond Sawyer (the private keeper who posthumously donated the koi and giant tortoises to the zoo).