Hypothesis: If I add different organisms into my compost pile, will it increase or decrease the rate of decomposition.
The independent variable being the different individual organisms, and the dependent being the rate of decomposition.
Explanation: This hypothesis ticks all the boxes. It may be among the wordier of the hypothesis, but it is short and sweet and to the point, compares the cause and effect of the independent and dependent variables, and aims to answer a testable question.