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Sorry, I don't think there's anything. Dwarf octopus can be kept in a 30 G, but I think 25 might be pushing it. Cephs produce a great deal of waste (far more than an equivalent size fish) and the water chemistry becomes very unstable in small tanks.
This is one of those areas that really depends on the details and on your knowledge as an aquarist. True pygmies (maximum mantle length under 3-4 cm) can do well in the right kind of 20 gal system, but it has to be single species, be well run in and rock stable, and hopefully have a small protein skimmer in case of an inking event. You also want to have a good supply of sea water in case of an emergency. We keep about 20 tanks, all under 20 gal, with a variety of pygmies such as O. wolfi, O. micropyrus, O. mercatoris, O. bocki , juvenile bi-macs and blue-rings. With frequent water changes the animals do well. However, these are research tanks that are pretty plain and bare-bones. They don't look good, but they keep the animals alive.