Cracks knuckles just getting some practice 
Advice on getting it to look more real would be great.
More randomness. Make some variations of shapes, rotate them in particle system settings, create more corals, use bump mapping and displacement for your coral base rock, look for tutorial of making realistic looking underwater in blender. Add mist, volumetric world, use depth of field maybe, and use compositor and photoshop. Glare, chromatic abberation, lens distortion, film grain, bloom, camera scratches. Also model some bubbles, find an interesting point of view. Experiment with colour, make something to grab people attention ad drag their eyes to some point of your image. And light. Beacuse I don’t see any lighting (looks like point lamp or something which is not good) 
Hope this helps!
Thanks so much!! i’ll get working on all of that i’m sure it’ll help it a lot