unfortunately they all cant live together...especially the frogs they absorb h2o through their skin and salt water would kill them immediately..as far as seperateing delicate fish from agressive with an island that can work but not with an octo...you would also need to add an extra overflow on that side...i am still concerned with the amonia spike and dont think this tank should have any live stock in it...it is your tank and you can do what you want with it but you should not put animals in that would surely be met with demise....just my opinion from someone who is trying to absorb as much information from great people who know more than me...take it slow and listen to people on this site that have far more experience than you and me please