I asked about the stuff growing in the tubes a little while back, from a different angle but the consensus seems to be that the crap growing in the tubing has little to no impact. Ive cleaned mine out a couple times and this white mung just keeps growing back. If I squeeze the tubes some feathery pieces break off into the water but they seem to be harmless and go away. Ive also been told that the bacteria growing in the tubing is not significant from a bio filtration perspective.
I did once have a stray piece of annacharis that got stuck in my tube once and grew to about a yard long. That affected the flow! I guess thats why I clean my tubing every couple months, so nothing like that surprises me.