when i clean the filter and then turn it on what is the white guck that comes out of the out flow

by russ mcgivern
(canada)

After cleaning my filter i am curious when I turn it on what is the white guck that comes out back into the aquarium. Is it from the hoses and does it hurt the fish or it sucked back in to the filter.
A: This is usually mineral deposits/organic material that clings to the inside of the plastic outflow parts. It is harmless but you should be checking water quality on a regular basis to make sure nothing is in the water that can harm your fish.