It should be the initial phase. Anyway, I just changed the filter sock that was collecting a lot of detritus from my return. So by tomorrow I should know whether as much detritus has been collected by the sock. Frankly I doubt it will be even 1/2 as much considering that my tank is really super clear now.
As for turning off the return when feeding, it all depends on you. In my case, I don't turn off the return. What I do is that I switch off all the wavemakers in the tank and that's it.
Lastly, cleaning the filter sock is really a PITA...
Hand cleaning is next to impossible as it is very difficult to turn the filter sock inside out due to the two plastic handles in the sock. After trying a couple of times to wash the filter sock by hand, I finally realised that the best way to wash filter socks is just to use the....WASHING MACHINE...
Seriously, using the washing machine, the filter sock is as clean as when it was new.