Is there any adverse effect on the water chemistry if a cinder block is placed in a pond as is with cement in the water?

Cinder Blocks in the Pond: I think that it would be harmful to fish, if you have them in the pond, because of the lime used in the production of cement. If it is to raise the level of a pump, you might try a terra cotta pot turned upside down. I have used ones with the bottom broken out for hiding places in the pond for the fish. (from egrets and hawks). Even adding city water with chlorine in it can throw off the eco balance in the pond.

of course, I guess the size of the pond is part of the equation as well... if it is bathtub size vs. the size of a house... obviously that will have some difference on the effects as well.