Bethany has a fish tank at her house. she uses the following data table to keep track of the nitrate and phosphate levels in the tank.

month nitrates phosphates
january 8.0 mg/l 0.010 mg/l
february 8.1 mg/l 0.010 mg/l
march 7.9 mg/l 0.009 mg/l
april 9.2 mg/l 0.012 mg/l
may 9.7 mg/l 0.020 mg/l
june 9.9 mg/l 0.029 mg/l
july 10.6 mg/l 0.032 mg/l
august 10.8 mg/l 0.038 mg/l
september 11.0 mg/l 0.036 mg/l

bethany notices that the fish tank is gradually filling with algae. based on the data she has collected, when did the problem most likely start? explain.