The last coral is a fox coral (Nemenzophyllia sp.).
Wayne,
Nice green eyed chalice. Battling colors on the two acros is nice, too

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A few things I've gone to on my xTI w/Sigma 150mm are:
Using AV setting on dial
Using f-stop back around 13-22 (unless going for a shallow depth of field)
Plenty of ambient light
Using a tripod and shooting perpendicular to the glass
(I don't do it, but would get a lot better pictures if i did)-Turn off all flow in the tank
Do a little post picture processing. I use Photoshop and typically just (Save For Web to reduce size) tell it to Image-->Adjust-->Auto Levels. That makes up for me under or overexposing the picture. You can adjust other levels, too, but it starts to be come obvious pretty quickly

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I am not as good with mine as I should be by now (have a lot better luck with the 70-200mm f/4.0 L IS). Those things have helped me take fewer bad shots

. Every once in a while I get a really nice keeper.