"considerable fluctuation" is correct and usable in written English.
You can use it to describe a large degree of change in a particular factor, such as in the sentence "There has been a considerable fluctuation in the stock market this month."
In the hundred years that have passed since Schoenberg's first premières, his reputation has undergone considerable fluctuation.
China is an important market, but it's a developing one, subject to considerable fluctuation, based on last year's figures.
This government has survived the full parliamentary cycle, but polling since 2013 has shown considerable fluctuation in voter support (see Figure 1).
By contrast, rates in the other regions have stayed more or less flat, although with some considerable fluctuation happening in the intervening years.
The evidence is mixed: demand for existing homes seems to be diverging from demand for new construction, and there is considerable fluctuation in prices and demand.New data released this week indicate, again, that qualified gloom about the housing market is warranted.
Baboons mate throughout the year and experience considerable fluctuation in food availability within and across years.
…including Dongting Lake and Lakes Hong and Liangzi, also causes considerable fluctuations in water volume.
Despite considerable fluctuations from year to year, Turkey maintained the economic advance that had begun in 1950.
The Caspian Sea has displayed considerable fluctuations in its water level during the past century.
The results obtained with BEFORE show that natural beech forests achieve quasi-stationary dynamics, demonstrating considerable fluctuations in the forest structure.
There have been considerable fluctuations in vegetation on the slopes and on the swamp which reflect both environmental change and anthropogenic influences.
