I’m guessing you’re the guy with the same name on reef2reef. You need a very well established tank (1 year +) for any cephalopod. Cuttlefish are a lot harder to keep than octopuses. No tankmates can be kept with either… the ceph will either eat them or become food. The tank I’m keeping open for an octopus has been running for 5+ years and is 70ish gallons with a sump. Not to mention octos are escape artists and dwarves especially can squeeze through the tiniest openings.
Neither of those options is large enough for cuttlefish. With the 20 gallon, you could keep a dwarf octopus with CUC- and actually have a pretty nice set up! I’ve really enjoyed O.mercatoris in 20 gallon tanks in the past!
As Hadla mentioned, no tank mates besides the cuc are recommended with any cephalopods.