I agree with Terry but I'm not sure on the boiling part.
What you can do is set up your tank first and your brick wall. I'm assuming your tank will be empty at this point. Provide a lot of water movement. Measure PH of your water when you first put your bricks in. Than measure it again 24hrs after. I would expect this to raise your Ph. If your Ph stays the same than your bricks aren't leaching any hardness to your water. IF there is a sharp increase than your bricks are leaching in your water. Cure bricks by dumping several cups of salt in your tank. Let it run for a couple days and drain tank, fill up with water and put salt back in. Do this for for two weeks. This should be enough time to cure your bricks. Do the ph test again.