I'm not sure why it's closed but, You go to this place not far off stoopolis and use dive then theres a cave, you go through it and go back to the surface, Then you keep on going forward and there should be a bunch of aqua members, After beating them and getting past them you'll come along Kyogre, and Archie will run up and stop you. Then the red orb wakes kyogre and you go to stoopolis , Kyogre and groudon are fighting , steven brings you into the cave opf origin to talk to Wallace, You tell him sky pillar. Then you go to sky pillar and wake Rayquaza he goes back to stoopolis and PWNS Groudon and Kyogre so they stop fighting. Then the gym opens, Sorry if I ruined some of the game for you :S
The Fortree gym.
there is no gym at pacifidlog
Defeat all of the Gym leaders on Emerald. ~KKMG1
there is no gym in slateport, the next gym would be in mauville with electric pokemon
In Pokemon Sapphire, Ruby and Emerald the 7th Gym that's located in Mossdeep City has Psychic type Pokemon.
In 7th gym
fortree
at the gym
The gym leader of Fortree City's gym...Specializes in flying type Pokemon
slate port does not have a gym
marshtomp
Water.