In my sig you will see what fish I have in my long 20g tank, well my common pleco started climbing the back tank wall (as he always does) but this time after he climbed to the top of the tank he somehow got onto the output of my whisper power filter 40 and literally started climbing the output part of the filter even with the powerful water flowing down him. So I lifted the lid to the filter he fell back down into the tank. Why in the world would he do such a stupid and dangerous thing? He has never done this before and has never been known to be a dardevil (except the time he jumped out of the tank). So is their a way to prevent this from happening again? And is their something I should treat him with even though I can't see any damage but can't see him real good because the light is off because I just added some more fish today and don't want to stress and scare the new fish? Any help would be appriecatied. 

Well he had never done it before and it seemed like he was stuck because by the time I heard the splashing noise and the time I got their he wasn't moving so once I lifted the lid of the filter he fell back into the tank. Well my second question is yesterday I added two more long finned black tetras and one more regular black tetra and ever since I added those new fish that made four for each fin type of black tetra he has become extremly active and is moving all over the tank it seems like the new fish have taken over his territory and when he tries to go back to his usual spot the new tetras chase him away and all the tetras are following him and he doesn't seem to like it at all because he is trying to get away but they keep following him while he tries to find a spot to claim his own. Will this problem sort it self out when the new territory is established or will this continue and result in me having to return the new fish from the 20g?
This is so stupid I hope he stops doing this once I feed him.