Gunge is what builds up in the mechanical filtration media. It's a bit smelly, being a lovely mix of fish poo and algae, but not especially toxic. Just rinse out the filters in old tank water as needed when you do your filter maintainance.
Toxins CAN build up in mechanical filter media IF you leave it in the water long enough. However if your servacing your filters on a regular schedule this shouldn't be a problem.
Your talking about Weeks before it can happen however so it's not much of an issue unless your a total slob.....lol
hey thanks, my originally white cartridge has turned grey, but is that still considered non-grotty?
I try to rinse the color of but it is impossible.lol