This graph allows me to investigate several things.  First, I want to compare the pH before and after filtering for each of our three filter types (cheesecloth, alum, and both alum and cheesecloth).  I see that the pH did not change when we used only the cheesecloth as a filter.  For both of the filters that included alum, the pH was lower after filtering.  These results show that alum is good for reducing pH, but a cheesecloth is not good for reducing the pH.  

Second, I want to compare the turbidity before and after filtering.  I see that the turbidity decreased a lot when we used the cheesecloth as a filter.  It also decreased a tiny bit when we used alum, but this decrease was really small compared to when we used the cheesecloth.  This suggests that the cheesecloth is better for reducing turbidity.