paint safe for fish

Question
we had a lot of concrete left over from another project so since our water garden liner had a leak we pulled it out and concreted our pond  now I'm told i will need to paint the pond or the concrete will kill the fish  Is this true if so what is the most  cost efficient paint to use as money is a big concern

Answer
Hey Karen it is true the concrete will kill the fish. I don't know about paint.How about putting padding down and putting a liner on top of the concrete. If you get paint I would think a color of dark blue or black. maybe some kind of swimming pool sealer. Thanks Eric