Bio media in sump

[slingfox]

Ya I'm thinking it is ceramic media that leaches IIRC. I'm not familiar with bioshperes, never had a reason not to use rock or rubble.

I agree with you that I would avoid most biomedia due to the leaching risk. Seachem Matrix I believe is okay since this specific issue has been looked into extensively by the freshwater and pond community and it is Seachem Matrix and the plastic based media which seemed to show no detectable leaching.