Well I have 2 oscars, 1 red and 1 tiger. They went from 1 inch to about 5 inches in 1 month! They usually average at about 1 inch of growth a month from what I was told. But it really depends on alot of variables, like diet, water, tank size and many other. If I were you I would check my water and do some research online, I also read they usually slow down at around that size. What size tank is your O in?