Slimey Stuff

[Night Crawler]

I have an external filter and inside the pipes there is a buildup of something. Absolutly no idea what it is.
Can anyone tell me what it could be?
Should I clean it out or should I leave it in there?
Its on the stones at the bottom of the tank as well.
Not sure about the size of the tank, but in it are 6 tetra neons, 2 clown loaches, 2 rainbow reds and a plec (cant remember which one)

 

[blue acara]

yep clean it out-over time it will reduce the flow of your filter. im not sure what it is exactly, probably dirt and algae. use a gravel vac to clean the stones.

 

[voo]

I dont know what it is either, but i've got it too. Everytime i restart the filter after cleaning it out it all comes out into the tank I cleaned out the pipe going to the tank so hopefully it'll stop it a bit.