Just to add my 2 cents, I have 3 Oscar's in a 125 Gallon with 12X filtration, I still have to do a 30% water change twice a week. And that is if I am feeling lazy... These guys crap turds like a small puppy and if I were to let it go for a month I have a feeling I would have a few dead fish on my hands. My PH is steady at around 7.8, and the fish have adjusted accordingly. They have arranged the tank to their liking and I have managed to make a compromise with them about the live plants I have not being in their way.
I have to say I would have no other fish if I couldn't have my oscar's, they are wonderful. But know what you are committing to before you take on this task.