sorry, but i dont have high hopes for this octopus. I feel that you dont have much experience with saltwater because 1. you put it in a tank with seahorses......Certainly not a good decision, it is going to suffer a horrible death, and has absolutely no hope of escaping an octopus.
2. the tank looks very small, and chances are that your octo. will get rather large, and i am absolutely positive that the top is not completely covered because you have a hang on back filter, with leaves at least a little room for him to squeeze through.
3. You have fake plants, and freshwater pebbles as the substrate.
I dont keep octos. so i am sure that there are 50 other reasons just from the pic.