I like to draw a gradient between medium and very dark blues from a top corner(light) to the opposite bottom corner (dark). This will be the "base layer." Then on a new layer I add very light (I use white) lines radiating from the light corner toward the dividing line in the gradient. I then blur the lines with a gaussian blur (between 10 and 30ish), then an unfocus blur (I use between 30 and 50).
Next I add a new layer and create some clouds with a very high scale and low roughness and Difference blending (like the fire tutorial). I set the layer to overlay blending and sometimes reapply the cloud effect if I want a little more of a satiny finish. I then merge the cloud layer and gradient layer.
I add one more layer with clouds again, same settings, but usually I don't run the effect more than once. I set the blending to overlay as well. This layer is to allow different effect when adding fish, rocks, coral, etc. I will change the base layer blending to something like additive or overlay, and place underwater object either between the cloud layer and base layer, or under both layers. I get some interesting effects.
I can't figure out how to add a picture...can anyone help me?