Attached Link: http://www.lysator.liu.se/~kand/caustics/

I think your caustics don't lok so good, but it's the gel's fault, not yours. If you used the Caustics generator, which is so easy to learn, then they would look a lot more real, imho. Render your caustics in grey shades, apply the render as a light gel, reduce the size of the image map to about 0.4x0.4 and see for yourself. About the white line, it's the fog, try reducing it, or lower it, and if it doesn't work, you will have to place rocks or terrains to hide it. To change the water colour, you can eitheir use the overall colour correction, and you get the colour picker, or right click the gradient to edit it, and in the newly opened tab, click the key colour, and you get the colur picker.