only got the info from Wikipedia on the net
... and chemistry, biology, anatomy , and all that related stuff were my favorites at school...
yeaah I know, this cartridge was disgusting
and because I could not get it clean I put a new one in.
( like changing nappies for a baby, lol )
and I did soak it in old tankwater only for a few minutes, maybe 2 the most.
I believe to soak it longer than that will use up too much of the activated carbon.
I also noticed that after vacuuming the gravel, the water left in the tank is pretty stirred up and cloudy. After filling it up with fresh water and starting the filter again, it was crystal clear in about 40 min to one hour