I really like keeping the red brittle stars. Most of the brittles are pretty nocturnal and reclusive but the red (more of an orange) will occasionally come out during the day. Most can learn to be hand fed. Brittles are very resilient and I have kept a number of the red for several years through multiple octopuses. Any of the serpents or brittles on this page would be a good addition (NOT the basket or regular starfish and especially not the Bahama star) and I have successfully kept all but the Bahama from this supplier. Mushrooms (but not Ricordeas) tend to be hardy, give a little color and are octo safe. Small crabs are nice but will become octo dinner. It is easy enough to get attached to some of them (don't ask me about the 3 blue crabs I have raised that were supposed to be octo food
).
I strongly recommend NOT adding fish as you grow the tank. Many people start with the very hardy damsels but they tend to pick on and stress octopuses (I am opposed to trying to keep octos with ANY fish) and are almost impossible to remove from a tank without totally tearing up the layout.

I strongly recommend NOT adding fish as you grow the tank. Many people start with the very hardy damsels but they tend to pick on and stress octopuses (I am opposed to trying to keep octos with ANY fish) and are almost impossible to remove from a tank without totally tearing up the layout.