Two layers of media: perlite in the top and 1/2" - 1" pumice in the bottom. Both were incredibly "dirty", covered with dust...which precipitated to the bottom.
Although I washed the material before using it, when I filled system with water, my fish suffered because of excessive water clouding.
Why were the fish there on the first place? I was replacing the media; previously had query rock which was affecting water pH...