Sorry for the slow response here and thanks for everyone chiming in - all great suggestions.
@Emerson, at the higher flow rates the RFG nozzle definitely need to be lower below water's surface. Depending on the flow rate, you will need to have the nozzles anywhere from .25" to as much a few 1.5" below the water surface - as measure at the educator end.
There are a few tricks can sometime help minimize them sucking in air:
The goal should be to minimize the educators (the holes near the back) exposure to the surface of the water.
- You can try rotating the nozzle so that one of the fins that separates the educator channels is pointed straight up. This sounds minimal but it sometimes is just enough to reduce the chance of a vortex forming.
- Next -you can make sure the nozzle is parallel with the water surface. Again, this serves to push the educators just a bit further from surface.
- Instead of parallel, you can also run the nozzle pointed slight upwards - like 5 degrees. In this case however, make sure you measuring the depth from the educators if you're worried about too much siphon back to the sump - since that's where the siphon will break.
- The other suggestions such as drilling a small 1/16in hole in the underside of the Y or in one of the loc-line knuckles to break the siphon earlier is good. Also, reducing or adjsuting the flow rate (if you have a DC pump) just a bit can help as well.
Other things to keep in mind - if you run wave makers in your tank, the water level over the nozzle may not stay consistant since the wave may raise and and lower the water level as the wave travels across the tank. In this case, you'll need to account for the drop when deciding how deep to run the RFG nozzle.
Hope that help and if you anyone has any questions, please do not hesitate to ask.