Are cement bricks toxic?

        I am planning on landscaping my 130 gallon tank.  I wanted to
elevate the back of my tank with cinder blocks so that I could
incorporate plants into my aquarium that emerge out of the water (river
hiasynths (sp?) or arrowhead in particular.)  An added bonus would be
that the fish that I plan to put in the tank could have nice little
caves to hang out in.

        My questions:

        Do bricks (either cinder blocks or the red ones) leach any
toxins into the water?  If they do, can I  pre-soak, changing the water
several times over the period of a week to remove the toxins?
        I suspect that cinderblocks will raise the pH of the water, but
I am not sure how much.  I am shooting for a tank pH of 7.5 to 8.0, will
the bricks raise the pH much above this?  I plan to purchase a CO2
cannister as a supplement for the plants - perhaps the two will offset
each other.

        Has anyone used bricks in their tanks without killing their
fish/plants?  I welcome you comments and advice.


buddy wiese
University of Michigan