Check your pipetting accuracy. This is important in every phase of LAL testing. Make sure you are adding the correct amounts of material. Good quality graduated pipettes are already calibrated by the manufacturer, but it is up to the user to use them correctly. So make sure your technique is correct for the pipette you have chosen. Pipettes should also be recalibrated at least annually. You can verify this by pipetting water on a suitable balance. This will show if the correct volume is used.