Pixinsight question about color gradient removal

[konstantinos75]

Hi

This is my attempt with Pixinsight of the Pelican Nebula.

http://www.albireo.gr/astrogallery/nebulae/diffuse/2015.08.20/Pelican.html

I did my best to process this image but what I don't like is the purple color gradient at the bottom of the image.

This problem appeared probably because I did something wrong with DBE, background neutralization, color calibration on the RGB frame.

Another explanation could be some bad calibration applying the FLATs...

Do you know how I can get rid of this purple gradient?

I am interested to remove this on the final image, and not go back and do processing from the beginning (make RGB , add L, Ha...)

This is the final FIT image you can download it here if you want to play 

https://www.dropbox.com/s/goqy6fyuronybkc/HaLRGB_final.fit?dl=0

Thank you