Adecreased ph coupled with a decreased plasma concentration of bicarbonate ion indicates that is occurring and the will compensate for this change.

A decreased pH coupled with a decreased plasma concentration of bicarbonate ion indicates that acidosis is occurring and the respiratory system will compensate for this change.  
Acidosis (metabolic) is a state when increased acidity in the blood occurs and it usually refers when arterial pH falls below 7.35. Metabolic acidosis may result from increased production of metabolic acids (lactic, for example) and is characterized by low pH, low blood HCO3, and normal or low PaCO2. Metabolic acidosis is compensated with an increased exhalation of CO2 to reduce metabolic acid.