hi I was cleaning my filter out fluval 305 external filter I cleaned it then put it all back together and turned it on and then loads of white stuff started to come out any ideas here are some pics.
Like Gidge says its just muck that's come loose while you were cleaning, its perfectly normal, it happens every time i clean my filter, it will clear up in no time.
If i knock my external filter by accident while its running, a burst of gunk flows into the tank the fish seem to like it.