Science Experiments

Question: Im want to a science fair project on the effect of PBCS on our water systems or ponds…but?

i dont know how to set up a testable experiment. im really clueless here, so any help provided would be appreciated. How could i test this in a manner that answers the question?
or would this question be more feasible: What effect does the presence of phosphates have, if any, on the oxygen level of water in a pond?

Answer: Go with phosphates/oxygen.

our completely dangerous science experiment