Hearing loss is cumulative, it is not only from exposure to dangerously loud things. I have some hearing loss both ears from normal exposure and a little more hearing loss in my right ear from dangerously loud things, m-16s and being a musician to name a few. I have to wear foam ear plugs when I play or my ears ring for days. Those pool balls are loud even during normal shooting. the pool balls themselves, in a pool hall type atmosphere, are probably not enough to wreak havoc on your hearing, providing that you are careful in other areas of your life. however when you get in an enclosed space, more of that sound energy is travelling through your cochlea and the potential for damage certainly is greater.
I would do as another poster said and put up things to absorb the sound reflections, much the same as in a recording studio. search online you can buy some dirt cheap foam panels and cover them with fabric or paint to match the walls.
You should also think about some form of hearing protection. I buy the 25 cent 3m foam ear pugs and cut them in half. I don't insert them all the way into the ear canal. I just push them in so they seal off the larger opening in the ear and seal the canal. This works great for playing pool. Blocks most of the ball noise but allows you to hear ambient noise well enough and allows to converse as you normally would.