I use an old Canon G16 in a Fantasea housing, with the G16's flash only, so a different brand but similar in the 'point and shoot' approach. I'm a snap shooter - I don't have the mindset, patience, whatever-it-is that empowers some people to do manual white balancing, manually set an aperture/shutter speed combo., etc...
But there is one manual thing I often do when snap shooting with this setup; I learned to turn the flash on and off. I tend to have it 'On' or 'Off,' not 'Auto.'
The flash makes very little difference unless the subject is pretty close, so even with clear water, if I'm zooming a bit to photograph something with some size (say, a big grunt, or a grouper) than won't let me real close), about all the flash is going to do is light up some backscatter and maybe annoy the animal.
On the other hand, if I'm shooting close and I want to bring out 'natural' colors (by surface lighting standards), contract flash-vs.-no flash depiction (e.g.: some animals stand out more against their background with flash), or just compensate for low light...then I want the flash to fire.
Unlike topside, what I seldom want to happen is for the camera flash to fire based on whatever the camera 'thinks.'
The TG6 is a different brand and later generation model, so perhaps you guys are happier with the 'Auto' setting for flash.