How to remove black aberation fringe in a black & white photograph

Hello, can anyone advise me how to remove a black fringe on the horizon of a BW landscape image?

I have searched you tube and Google and these forums but the advice given relates to chromatic aberration in colour images. 

I started with a colour image, removed the CA in Light Room and then took the image to Photoshop for editing.

I removed the CA again using the common method (Gaussian blur/ colour blending mode) which worked fine, but as I have used a lot of editing & layers to change the image to BW, the fringing has reappeared as a black line.

I tried the method stated above but that did not work with the BW image.

My work flow used Nik/Google software: Define 2, Viveza and then Silver Efex.

I saw a few comments that the fringing is caused by over sharpening however I have NOT done any sharpening.

Can anyone offer some advice?