Thanks for all the advice. I was shooting with the wide end of a Tokina 10-17 and got as close in as I could and still get the arch in full. I have some much more colourful shots in close where I could get strobe lighting but don't show the whole scene. I was wondering if there was some trick with white balance or something I had missed but I guess I'm just asking for the impossible (I'd love to try off camera strobes but could be difficult as this site is very tidal and in 30m). As for buddies in colourful clothing the only person I know who has one dives with his wife - although have potentially found one with purple and yellow drysuit!
Yeah, agree, too much landscape, too little light. I think you could cheat your ISO a bit higher, lower your f/stop. Get in tighter and widen the lens.
But what you could also try is to have your buddy light the desired element with their dive light, providing a bit of "off strobe" light. It won't be great, but to the eye it may look natural.