Thick white film coming from return pump on start up?

[CrazyKoiCracker]

Planted 50 gallon lowboy.
Overflow/sumpfilter
Ph 7.4ish.
Ammonia/nitrites 0
Nitrates 20-30ppm
Injected co2, 4 bps
Weekly doses of sea chem flourish comprehensive and iron.
Aquaterra sand and fluval stratum
Malaysian drift wood and dragon stone
Stocked with
4 juvenile bichir, three Delhezi and 1 Senegal.
1 bristle nose pleco
1 spotted Raphael cat
7 Congo tetra
3 Odessa barbs
A handful of home bred guppies
I know the guppies at least will likely end up snacks as time goes by.
Figure I’d get all that out of the way Incase anyone asked.
Now on to the question.
Once a day I come home for lunch. Cut the return pump off, and feed.
If I don’t cut it off I just end up feeding the filter sock.
After about 15 minutes I turn the pump back on and clumps / strips / sheets of a beige film/slime comes shooting out of the return. It’s gotten worse each day until it turned my tank into a snow globe a half hour ago. I netted out the bigger chunks and after the fact thought photos would help so there are a couple photos of some of the pieces I missed in the tank.
I’m probably just going to the store this afternoon and getting a new return line.
But what is this junk? Why all of a sudden? Causes and prevention?
Fill me in please, and thank you.

 

[deeda]

It's just a combination of bio-film, gunk and other stuff that builds up in ALL filters/parts and turning the pump off and then on again forces stuff to flush out.

Just clean the hose or piping with a filter tube brush or a small piece of rag attached to a flexible wire or a metal coat hanger if it will pass through any elbows.

 

[esoxlucius]

Yeah, as already mentioned it's just bacterial gunk and film that builds up in the lines. It's fine when water's flowing through but when you stop your pump for feeding or maintainance, and then switch it back on after, well, you've seen first hand what happens.

It's harmless, just damn unsightly and a bit annoying, especially if you've just vacuumed during maintainance and then all of a sudden your substrate and water column are full of crud again.

The only way of really preventing it is to clean your return lines regularly. I use thick baling wire from work. It's curled up at the end into a small hook where I attach a small piece of rag. Then I drag it through the line and it drags all the crud out. Some people say that using clear return lines can add to the problem as light can help with the build up of the bacterial film.

 

[CrazyKoiCracker]

Thanks guys. I figured it was just a biofilm but the amount being flushed in has probably tripled each day. Can’t make it to the store today but amazon is an amazing thing.