If your testing chamber is overflowing, the draining pump could be the issue.
You need to do the following
1- Remove the back acrylic panel
2- Remove the pump head of the 3rd Blue peristaltic pump to the right ( the one besides the orange pump) : by pressing on the two plastic bits on the left and right of it and applying pressure to the top to unplug it from its base.
3- Replug the same pump head but this time do not plug all the way in, just make sure the pump head is hooked to the axis of the motor. ( there should be like 4 to 5mm space between the back side of the pump head and the base of the pump)
4- Run a Test
When the Reefbot is supposed to drain the Tank water, the pump should start running and the you should observe the pump head being dragged down until it gets plugged by itself.
If the pump didn't run at all it means that the connector is not plugged correctly. Unplugging and replugging the connector should solve the issue (check arrow indicated in the image below).