There are a number of signs that may indicate your fire sprinkler system has MIC:
Black Water or Red Water
By products produced by the bacteria associated with MIC affect the color of the water.
Foul ‘rotten egg’ smell
Sulfur related bacteria can be part of a MIC colony and produce hydrogen sulfide gas and its distinctive ‘rotten egg odor’.
Iron related bacteria remove iron from the pipe walls and create small pits that grow into pin-hole leaks. Other acid producing bacteria make the problem worse by further degrading the pipe walls.