Balrog

My eye wanders around this image too much and the lighter coralline branches lead it off the page. A health dose of 'fist' (vignette) will probably give the subject more punch no matter how you crop or colour balance it.

I think its all in the nature of your approach.

If they are snoozing, they often get surprised and take flight when they spot you.

If they are swimming its difficult to approach other than on a broad arc without appearing to be chasing them - a fruitless effort.

If they are feeding its possible to approach casually and allow them time to conclude that you are not a threat.

So, yes, when feeding is the easiest time to get close up and intimate.

After a trip, I dunk my domes in a sink full of water with a small amount of detergent on the basis that it will flush out any grit etc that may have found its way in there. Rinse, then dry the dome, as suggested with a microfibre and leave it dome up for any residual water (on the inside of the flange) to evaporate rather than run back onto the glass. 

I did the same thing. Got under to find the cable and housing not connected.

There was some corrosion/missing plating on the pins, presumably electrolytic action. I just flushed well with fresh water, dried thoroughly and put a smear of copper grease on the pins to ensure a good contact in the future. 

Still working fine 3 years later

A balloon, tied off with the slightest puff of air in it could give a good indication of vacuum retention.

Good luck getting it through airport security