Help needed - wide angle autofocus settings for Canon 5Div in low-light conditions

My images had been pretty sharp until recently, but now I've had a month or so of very out of focus wide angle shots - so soft and out of focus they are unusable. 

I suspect this is because myself (and someone else) changed the settings in my Canon 5Div and/or the conditions I'm trying to shoot in (low light, deep wrecks - inside and out).

What would be the best Canon autofocus mode and autofocus area mode settings for shooting fast moving schools of fish (inside and outside wrecks), wrecks in general and divers swimming amongst the wrecks and fish?

 First, you should make sure your camera is working correctly by shooting some images outside of the housing. Make sure to also test at reasonably low light levels such as those corresponding to those pix that failed. I would shoot in single shot AF mode so that you can observe the AF points. As well, turn on the beep. You may also turn on focus priority. Are your pix still out of focus?

Just to clarify you say that  settings and/or conditions may be different, have you done low light shooting successfully in the past?  Wide angle lenses typically have quite good depth of field and fairly snappy to focus, so they need to be along way off on distance before the picture is completely out of focus.

Typically the suggestion for AF is to use a single AF point in continuous AF using rear button AF and re-composing if required.  Definitely confirm the AF is working on land.  I'd also suggest looking at a few images to see which AF point was used - Canon software can do this as can Breezebrowser but I don't believe PS can do it.  You may be able to see if the AF has snagged something other than your intended target.