hi everyone. i'm fairly new to fish keeping and i currently have 2 fire eels and a silver aro in a 55 gal tank. i just bought a 600 litre tank to house them in and it will arrive in 5 weeks time. i also bought a fluval fx5 for this tank. i need some advice from the wise people on this site on what ti use as the best filter media for as my set-up for my fish. thanks and all advice will be greatly appreciated. 
