do I need a filter in a 5gal nano? I will (hopefully!) be keeping neons and corys in there... so i presume i do need one for the fish, but im not sure... wont it decrease the CO2 for the plants? and if so, do i then need to make a CO2 kit? I will more than likely have elodea densa, eleocharus parvulus, mini amazon sword, bacopa monnerii, vallisneria torta and rotalla indica in there. maybe sagittaria natans and aponogetum crispus if theres room!