How far open should you have the valve on your bubbler in your fishtank?

The valve on your bubbler in a fish tank should be adjusted to create gentle surface agitation without causing excessive turbulence in the water. A good starting point is to open the valve halfway and then fine-tune it based on the needs of your fish and plants. Observe the behavior of your fish; if they seem stressed or are struggling to swim, reduce the airflow. Conversely, if there is insufficient surface movement for gas exchange, gradually increase the airflow until you find a suitable balance.