If you look in the pictures, you will see brown stuff growing on the bottom of the filter cabin and lots of white particles on the blue filter!
My filter still works fine with no issues.
What is that?
It that ok for the tank and the goldfishes?
Is this stuff good bacteria?

I believe the brown stuff is mulm, a mix of bacteria and organic matter (poo and uneaten food). Although it is not harmful outright, if it builds up, it can impead the filter flow. The white stuff looks like mineral deposits from hard water.