Make sure you are rinsing everything you put in your tank before it goes in. If you want to make sure its clean you can add a little bleach to a bucket and soak the object for 10 minutes, rinse, and let it dry before putting in the tank. I imagine the glass paperweight would be alright in the tank. The geodes might cause some chemistry problems over time depending on what the rock on the outside is comprised of. In aquariums, the decorations are mainly concrete and the concrete does tend to leach chemicals in the water after a few years. However, these chemicals often make the tank more basic which is helpful in saltwater systems, especially if topping off with freshwater is needed. Its sort of a self-buffering system. As far as how much time it would take to start causing a problem in your tank its hard to say. You can try it, but I'd run a chemistry test at least once a week for a month or two. If the numbers are consistent then I'd do a full chemistry test at least every month to make sure the water isn't going too basic, which would be what I would expect the geodes to do over a long period of time.