I know very tanks with have SUMP in planted, but have a big problem, u lost many CO2 because the fall caused by sump, so its a option
If the tank was very big thats in the best option think in cost, but if u can afford a canister its better becouso u dont lose CO2
Im planning something simmilar.but the sump is gona be planted as to aid in filtration.
And the main tank will have a few plants only as it will hve oscars or silverdollars in.
If you do the sump root mabe try injecting co2 into the sump return pump,maybe giving the co2 maximum contac time with your main tank and only losing co2 when water travels back down to the sump.
It all depends on what your plannig to plant i guess.Your best bet wil probly be planting plant that doesnt need high levels of co2.something like java fern.
I'm planning on doing a sump on my 160g planted tank that I'm building. If you keep the sump closed it will help out in the co2 loss. you may have to increase the amount of co2, and have the co2 injected on the return side of the pump like jaxbr said
im planning to use glosso stigma plants only.
if i use canister filter,the pipes would be seen. and i dont like it to be seen.
thank you very much guys