My local fish store is having their every other month sale of $1 per gallon regardless of shape, and I am considering picking up a 40 gallon (around 151 liters) breeder tank in order to set up a Dutch style aquarium, which is a style I've always wanted to try. (Note: No affiliation with the link, just a decent article on the style.)
I will either get a 20 liters (around 5.3 gallons) tank as well and build a trickle filter into it, or get a used one from another LFS that sells used marine tank equipment.
With that style of aquarium, CO2 injection is almost mandatory, but what I would like to know is if the CO2 injection has to be into the tank, or can it be done in the sump? I would assume that it could be anywhere, but I don't know for sure. I'd prefer having as few tubes running into the actual tank as possible.