Observation and thoughts on my Kratky with 6 inch net cup bucket cover in comparison to my 3 inch net cup Kratky bucket cover. The roots in my 6 inch net cup are not as robust as my 3 inch net cup, the roots in my 6 inch net cup look like they are being air pruned. I think the bigger net cup allows more moisture to evaporate, so the air space isn't as moist as the 3 inch net cup space.
I was kind of forced to keep the solution level touching the bottom of the 6 inch net cup as the roots were not keeping up with the evaporation. I have grown them like this in my first trial, but was thinking I needed a 3 inch air gap on this new trial, but the size of the cup had a significant difference in the plant roots, so I will switch to 3 inch net cups or try covering the top of my 6 inch net cups in follow up Kratky grow outs.
However, I don't see this problem in my hybrid Dutch bucket system with constant water flow on top. The water flow sucks in air and keeps the air space moist, so the roots don't air prune. There is only a constant 3 inch solution level in my hybrid Dutch buckets and the roots in this system keep growing until it reaches the 3 inch reservoir.