You need to test the antler in a separate bucket of water so nothing in the tank affects the pH reading.
Get 2 buckets and fill them with tap water. Check the pH on both buckets and write the results down. Put the antler in one bucket and leave it there for a week or two. The other bucket has nothing but water in and is the control. Monitor the pH on both buckets during that time. See if there's any difference at the end of a week and two weeks.
Get 2 buckets and fill them with tap water. Check the pH on both buckets and write the results down. Put the antler in one bucket and leave it there for a week or two. The other bucket has nothing but water in and is the control. Monitor the pH on both buckets during that time. See if there's any difference at the end of a week and two weeks.