leeching

Hey guys so... i've seen some ceramic bio cube thingys on ebay which i'd like to put in the first chamber of my Evo but dont know if they'd be able to leech anything into the water possibly? ill add a link at the bottom if anyone wants to check them out, i think they look okay and i definitely...

So I’ve done some more research into media for tanks. And ran into claims marine pure leeches aluminium into the water especially if moved. Does anyone have experience with this? And are the mantis blocks a good alternative?