in the sceanrio where the waterlevel will be low enough that the pump will run with a lot of air bubbles, you have two main actions which will appear:
- The flow will decrease dramatically
- The pressure right behind the second pump will decrease dramatically
Both actions you can measure and control with Sensors AC will offer you.
Also you will have an audible difference caused by the air. But even you missed that, your pump will not run completely dry*, so no worries there until the alarm action of an aquaero kicks in.
*Don't qoute me on that. You should not run the pump in this state for a longer time than necessary to shut down the computer. Without draining the pump by dismantle, you will have enough water for emergency lubrication**
**Don't qoute me on that either