I would second the lack of rock opinion, they do like to hide a lot, but at the same time, if you want to display your octopi, you want it to have one or 2 hiding places, and that's it, otherwise you may never see it. I don't know if you've also covered the overflow strainers with mesh, but that's a perfect place for your octopi to escape as well. Also, even if you have, they are not averse to climbing up out of the water and over things, so if your overflow doesn't reach to the top of your tank, they might have crawled over it. Didn't mean to imply any insult, I just think that marinedepot screwed you by selling you 2 octopi to put into one tank. To address Mouse's question, I don't know of any species of octopus that you can keep more than one of together. Certain squid and cuttlefish and nautilus can be kept together, but out of the cephalapods, I don't think there are any octopi that can be kept together. Even different species will fight, and an octopus will attack pretty much anything that moves, like I said before.
If you did spot a tentacle, I think you're on your way to having nothing else in your tank. The problem with most octopi is that they are nocturnal, and training one to come out and do stuff in the daytime is difficult. The species that are active during the day get too large for the home aquarium. I think the blue ring is also a day creature, but it's also very very very lethal. I had one years ago that I only saw a couple of times, and it died after 2 weeks. It came by accident instead of what I ordered, and when it died, I was so paranoid about the neurotoxins that I drained all the water out of the system and replaced it, just in case it had released its toxins into the water.
Anyway, if you do find one, there are a couple of places on the internet that sell bulk fiddler crabs which can be a good food for it. They also sell various saltwater shrimp as
feeders, and also silversides (although they come as frye). I placed my first order with one of these places today, and should receive some mysis shrimp tommorrow. However, the mysis are probably too small for an octopus to bother with, although if it's hungry, it'll eat them.
Again, hope it's alive, and good luck. If by some chance you have both alive, seperate them. I would consider buying those oceanic cricket cages (look like tiny lizard lounges) and submerging them into your tank and housing an octopus in each until you figure out what you are going to do. Also, put them on opposite sides of the tank so they don't ink at each other. A cheaper alternative is a critter carrier (those little plastic habitats with the mesh tops).
