Is cement mortar harmful to fish? If so, how to deal with it. Thank you, hero

Cement mortar is very harmful to fish. The main reason is that cement mortar is very alkaline, similar to lime. If it is a cement pool, it is recommended to soak the fish in water for more than 1 month before releasing them, and change the water several times in between. Adding acetic acid or calcium superphosphate in soaking water can accelerate the decrease of alkalinity.