As mentioned above, it's hard to predict. If it truly is diatoms then there is not much you can do other than wait for it to run it's course.
On the other hand if the tank is four months old, it could be other types of algae. My advice would be to post a pic of the tank and as much information as you can provide about it. There are a lot of experienced plant growers here that I am sure would be glad to share their thoughts and help you out.