Fault

Possible Causes

Wrong pH value.

pH test carried out above 25C.
Overheating through prolonged sterilisation, remelting or overlong period at 50°C.
Incomplete solution of medium.
Poor quality water or containers.
Dehydrated medium stored incorrectly or beyond the stated shelf-life.

Turbidity, precipitation.

Poor quality water or containers.
Overheating or prolonged storage at 50°C.
pH value incorrect.
Incomplete solution.

Darkening.

Overheating, incomplete solution or pH drift.

Soft gel.

Agar not in solution, poor mixing, prolonged storage at 50°C.
Overheating at low pH values.
Error in weighing or overdilution with inoculum or media supplements.

Poor bacterial growth.

Prolonged and excessive heating, incomplete solution.
Inhibitory substances in water or containers.
Possible Causes
Darkening and pH drift.