Are you putting the foam in the tank under the rocks? Because I believe the foam is gonna break down and fast in the water with rocks placed on it and just make a mess. Also the rock your showing doesn't appear to be shale in my opinion and unless your certain you shouldn't add it to your tank. Remember a lot of rocks can have buffering effects on the water and can play havoc with your ph which would be bad for the fish. If you can confirm the id of the rock and won't have any effect on the ph you can add them.
