Eco Earth is perfect. Is is what just about everybody uses, eith er that or another brand, but the product is the same. If it is muddy, then you need to squeeze out the excess water. I put my brick in the water to expand it, then I squeeze out all the excess water that I can, then I leave it sit out for a week to dry, turning every now and then. While still slightly damp, I pack it into a cage, to form a compact substrate. This will hold up to a burrow much better than just throwing it in loose.
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KJ Vezino
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Missouri Tarantula Enthusiasts Group