Couple newbie Gfo running in a reactor qs

[Timbits]

Experts! I'm still a noob on this subject.

1) I notice the Gfo tumbling at the top/surface really well, but not moving at all underneath. Is all the Gfo suppose to tumble? Even the bottom?

2) if I test the water coming out the reactor, will it measure 0? If it doesn't, then does that mean I need to change the media.

3) how often do you clean the glass with fresh media. I know some ppl use that as a sign when to change it. With fresh media, do u still have to clean the glass every few days?

Thanks!