Variable overflow possible?

[Gjn]

I have a horizontal PVC hydroponics system that currently is a drip system. I'm thinking of converting it to a 24/7 system that maintains a certain level of nutrient water. The thought was simple - incoming water on one side and a "variable " overflow on the other so that the level of water inside the PVC can be adjusted. An Aerator is being utilized in the storage area.

1) is there a way to have an adjustable level of water (4 inch pvc)? One of my thoughts was a valve on the output, but that doesnt work too well because of sediment if I place it on the bottom. Also the valve isnt sensitve enough.

2) Any problem with flowing water 24/7?

Jerry