Well it does leach back, and have yet to see any evidence showing it dosnt. Think about it, carbon breaks down fairly fast, and as it does the stuff absorbed isnt going to absorbed substance heaven, it goes where the water flow is going, back in the tank.
Given how fast carbon breaks down i cant see using it as a bio media as being a choice of intelligence, i'm sorry but that just seems pretty stupid to even consider using it. Which is why it is known to leach detritus back into the tank only after a few weeks. It isnt effective as bio media, and given the choice of other options out there, which are cheaper, and dont break down it should never be considered.
I suffer from MTS & have a little bit of everything