Black Sea

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The composition is great! It`s a good use of gradient filter... But in the sky... I`d love to see some more vivid colors. Use some PS: select the sky, apply some levels and, if necessary, push up the saturation a little bit. This way the light/colors will be equilibrated in the composition... IMHO...

I like the background more than the foreground. I think that if you cropped out the very bright algae-like structure, you will have a more mysterious, intriguing photo. Regards.

 

PS: after cropping and slight increased saturation.