@Neogonodactylus - thanks for the review. The video has me wondering about
hummelincki except I don't see eyespots and the suspected origination location would be wrong (most hummelincki we see come from Hatti and a few from south FL). The white "skunk" stripe and the "cone head" posture are something we see a lot of species display so it is not helpful for identification. You can
search hummelincki in the titles on the journals forum to look for similarities.
I would like to reinforce ALL of
@cuttlegirl 's recommendations. You will note from many of my other new keeper posts that I STRONGLY advocate for NO FISH in an octopus tank. Damsels or wrasse both tend to be aggressive toward octopuses, may peck at them and definitely keep them on the defensive and stressed.
Here is a link to some of the positive and negative tankmates. Adding more CYCLED live rock (and the rock in your sump should be cycled) and places to hide will help reduce stress but be sure you give it places to hide - if you can see it, it is not well enough hidden. As the animal becomes more comfortable (removal of fish, again, required) it will likely allow you to see it but it NEEDS the ability to hide.
As far as tank maturing goes, three months of active cycling (adding additional biologic load the whole time, I prefer to use live rock, clean up crews and over feeding to accomplish this) is generally considered a minimum time for building up enough bacteria to handle the biological load of an octopus. I know the pet stores tell you a month and that you likely had your water checked but an initial cycle is only acceptable to handle the biological load of a few small, hardy fish and they often, unfortunately, recommend damsels. It takes much longer to accommodate larger animals (something they never explain or sometimes know and is sadly the reason for
New Tank Syndrome). It is good that you have a 72 gallon aquarium and sump as the quantity of water will help but your denitrifying bacteria will not be mature enough for handling the waste. Keep a close eye for any ammonia. I would recommend 5 gallon water changes twice a week to help keep ammonia and nitrites in check (you should never see a registration of either). If you don't have a reagent kit, buy the strips. They are frowned upon by many but will give you quick readings for nitrite. Ammonia tests are separate but there are inexpensive kits easily available to be able to monitor - be sure you use the external vial and don't test in the tank.
For feeding, I have found this sized animal very easily accepts blue crab claws that I find at my local Asian market. I pick out claws that are already severed but still fresh and freeze them. Thawed table shrimp is also often well accepted. Fiddlers and sometimes snails will be eaten but are expensive and multiples per meal would be required. You can also offer an opened clam (any mussel is acceptable but I find clams to not foul the tank where mussels and oysters make a mess). I usually keep live clams in the tank. Sometimes they are eaten but once the octo is accustomed to easy food, they are often left alone.