There are 4 possible causes.
The first is the pump is just a bit dirty, this was an unintended feature but if the pump is a 6000 or 6101 or 6105 running at 12-15V and the pump is slightly jammed, it will draw more power and starve the controller so it only goes to 80%.
The second possibility if the pump is that either the driver or connector speed adjustment has been turned down, the pumps must be set at full power on the driver box or connector box if a controller is being used.
Another possibility is that the cable or sockets are corroded.
The final possibility is that the resistance to the LED's is too strong, it is a permanent resistor and not variable. In this case the controller actually is going to 100% but the final LED read out bar for 100% cannot turn on.