Question
Is concrete acceptable material for lining a pond? Seems more permenant than a liner and would form a good base for mortar and rock features (waterfalls). I've considered adding some black dye to acheive the same color effect as a commercial liner. Would fish be hurt by rubbing against it perhaps?

Answer
Hi,
Most koi ponds are made with concrete including mine but some are then lined with fibre glass, as long as the sides and bottom are smooth and skimmed with a waterproof agent in the concrete to make it water proof, you will have no problem.
my pond as been in use now for nearly thirty five years with no problem, you can see it on my website at http://koi-z-are-us.20m.com
George.