Your octo is in a 2 gallon eclipse? That's far too small, even for a small octopus.
A briareus will eventually have arms 2 ft. long each. It's going to be too large for a 30 gallon tank, too.
Where are you getting your water? - you need to use water purified by reverse osmosis (RO)and preferably deionization (DI) before you add the sea salt mix. Or are you just getting sea water from the ocean?
Do you have test kits for your water and some way to measure salinity and pH?
I think you should consider returning this octo to the LFS or to the ocean, wherever it came from and then looking into what you need to keep an octopus successfully. We have articles on our Ceph Care page (click on the Ceph Care button above).
It will take some time to gather everything and cycle your tank, but then you will have a good place for octopus to live. Keeping a salt water aquarium, necessary for keeping salt water inhabitants, is not easy, simple or inexpensive. However, many of those who take the time and effort find the results worth the trouble.