Personally have experience with both the Octopus will only live for less than a year especially small species. Octopus are extremely intelligent so don't be fooled by their look. The smallest gap will become an escape exit. Fed live fiddler crab and whole market shrimp from wooden skewer.
The Angler fish aka frog fish was kept with larger tankmates at the time and was fed live goldfish but during those years didn't know that over feeding could result in premature death until reading something on the frog fish last year. A 30 gallon is too small for either due to both species bioload. Btw there are a freshwater specie of angler fish available just in case you didn't know that.