Amigos,
Filters even with a high end SLR are useful only in bright light and shallower depth. They WON'T replace strobes for bright eye popping colors in my opinion.
You need to boost your ISO even in bright tropical conditions to at LEAST ISO 400 to keep a high enough shutter speed that minimizes blurred images.
I have shot with both the Magic Filter and also WHITE BALANCING at depth off my hand, sand, or white slate.
Many times I LIKE the effect versus strobe lit shots (or when shooting too far away where even the most gigantic strobes won't add any color.)
The biggest tip is to re-calibrate your white balance if you change depths of maybe 10' or more deeper or shallower.
Here's some samples.
dhaas
David Haas Underwater Photography
Filters even with a high end SLR are useful only in bright light and shallower depth. They WON'T replace strobes for bright eye popping colors in my opinion.
You need to boost your ISO even in bright tropical conditions to at LEAST ISO 400 to keep a high enough shutter speed that minimizes blurred images.
I have shot with both the Magic Filter and also WHITE BALANCING at depth off my hand, sand, or white slate.
Many times I LIKE the effect versus strobe lit shots (or when shooting too far away where even the most gigantic strobes won't add any color.)
The biggest tip is to re-calibrate your white balance if you change depths of maybe 10' or more deeper or shallower.
Here's some samples.
dhaas
David Haas Underwater Photography
I do know how to set a manual WB though. I have a slate for that as a matter of fact. 
