I'm using the following setup to pump water out of a space below the gravel (yellow) in my aquarium:
The tubes displayed as lines are 12/16mm silicone tubes. The pump is a 300l/h electrical water pump.
The problem with this setup is that the biological filtration creates nitrogen compounds. They appear in large bubbles under the gravel which are sucked into the pump. After days the pump starts to run rough because it's not made for handling the gas bubbles in the tube.
I'd like to keep up this setup which is ideal with the exception of gas bubbles reaching the pump. Is there any way to separate the gas from the water before it reaches the pump inlet? A component? A smart arrangement of tube?
The relative height of the pump to the water surface, suction end of the tube or buttom of the aquarium can be modified in order to achieve a solution. I tried to have the pump on the same level as the aquarium as well as a slight elevation which seems to increase the time until the pump starts running rough a little bit.
I'd like to discuss the engineering problem rather than the aspects of running an undergravel filter.