Carpet pad is made of pieces of sponge glued together. I will absorb and hold water, the perfect growing conditions for mold.

Sand or vermiculite is used so the water will drain into the ground instead of holding water and growing mold.

thanks for the response, makes sense. just trying to come up with a less labor intense solution...the pool is 12x24, a lot of sand! took forever to do the smaller round pool, and now we're upgrading