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Now your bubble is ready. Convert it to Smart Object, for making endless transforms :). Click on this layer with RMB and choose Convert to Smart Object.
Now duplicate your bubble (drag and drop layer to "New layer" symbol) then transform duplicated layers (Ctrl + T). Repeat it a few times.
If you have too much layers, just click on some with holding ctrl. Then click on chosen layers with RMB and pick "Convert to Smart Object". You can freely transform group of bubbles.
You can also play with smart filters. I've used from top menu Filter > Blur > Gaussian blur...
Now, for making colors good, add adjustment layer with Gradient fill.
Change blending mode to Overlay, decrease opacity to 20%.
I'll show you, how to make your image deeper. Add new layer. In your color picker set green and black colors. Then, from top menu choose Filter > Render > Clouds.
Change blending mode to Soft Light, also decrease opacity to 20%.
Then, from top menu choose Filter > Blur > Gaussian blur...
This step is optional. Add new layer. Pick Sparkles brush and draw some sparkles around your mermaid. Use white color.
Set blending mode of this layer to Soft light. Layer will inherit colors of the rest of image.
Again add new layer. Use the same brush (Sparkles, white color) and set bigger size. Draw some strokes around tail.
Now set blending mode to Vivid light. Decrease opacity to 33%..
You should fix Brightness/Contrast. Add Adjustment layer.
Optional - add Hue/Saturation adjustment layer. It will fix all colors.
In your color picker set as primary color some green or blue (as your wish!), add adjustment layer with radial Gradient fill.
At the end, change blending mode to Multiply.