There's a post put up by Xamel on a excellent sea bed dio in this link below:
Hauptman's ChampagneIn that link the maker of the dio explains briefly how he did the dio. I have not done one myself so I'm afraid I can't help you all that much. But I do know most effective sea beds dios involve mostly 2 parts.
One the sea surface which is done usually using either a glass or acrylic sheet. Artist gel or other transparent, water-making products are tinted and added to the top to create waves. The second is the portion below the surface. I've seen some using resin and gel and others using tinted glass. I prefer tinted glass because its less messy, faster and very effective. In the above dio if I'm not mistaken the maker used smoked or tinted blue glass.
The amount of paint you tint the layer at the sea surface and the number of waves will determine how much overhead light will penetrate. This will then have a strong influence on how realistic the sea bed will look. Experiment a bit first with tinting, waves under a light source to see the patterns and color it creates first. Not sure if this thread below will help with the surface:
Making sea surface experimentsGood Luck and post some progress pics if you can.