http://cch2o.com/under-current-instructions/
Page 31 - it's a PDF file. But this is what I'm going with after having root issues in that air gap space. It makes sense now too - as long as it's got plenty of O2, the roots basking in the nutrient solution keeps them clean and healthy. While it's dangling in an air gap, I'm thinking that it's not going to be exchanging as much nutrients and water as it could if it were submerged.
Also bottom line for me... I had issues when the levels were below the net pot. I followed UC's directions, now the roots are healthy. On other forums people have basically called me stupid for keeping the levels this high. One guy swears that it's a design flaw and that all Under Current systems will fail because of this. Ok...
This is what I've found works for me.