i have a 30gal rectangle fresh water tank with a penquin bio filter the bottom of the tank is gravel the fish in the tank areas follows; 2 black tetras 2 aero tetras, 1 spotted placo, 2 cory cats, 3 new guina rainbow, 1 female and 2 male, 1 blood gourami 1 blue gourami , 1 rainbow shark, 1 bala...