i have similiar setup as you using 2 filters. one purely for filtration that which is also hook up to the chiller.
The other is purely for CO2 distribution without filter media as i think if the plants are doing well, they are the best water purifier you can get in the tank.
thou my tank is just 4x2x2, i am facing CO2 distribution issue which i think that is the reason why my HC are not growing. i was using lily pipe with ceramic diffusor place at the opp. end from the pipe outlet. i tested my pH but it wasn't dropping to my desire measurement after increase the injection.
thru the help of my neighbour, i diy a external CO2 diffusor and created this (see pic) last nite. hope i can get my HC growing.......
