Your Canon can get awesome pics. I use a Nikon D40X- pretty equivalent. I have tried the ISO up, but not been as happy. I leave the ISO on auto, pull the tank lights all the way to the front, use a macro setting, leave the flash on and shoot at an angle to the glass. I have found the most important things to be the angle to the glass and the distance of the fish from the glass. If they are more than 6"deep to the glass, I don't bother shooting them. The water really blurs. A little experimentation will let you know how shallow of an angle you get away with without a flash flare. I also sit pretty close 12" or so from the glass. As always, the more contrast the fish color has with the background, the better your final image will look. However, the macro setting blurs the background, making a lack of contrast less obvious. Fast ISO and adequate light allow tack sharp detail. Entire tank shots are miserable for me because all this advice doesn't work. That requires a tripod for really amazing shots.
I vary my use of the autofocus feature of my lenses. Its really hard to get it to focus on a fast sword fry, so I resort to manual for babies. All I have to say about shooting fish is thank God for digital because it takes alot of shots to get the one that pops.
Black fish are also a real challenge. My black angels are really hard. The flash shows their amazing irridescence, but inherently over brightens them. They don't look black. The pics are pretty, but don't accurately depict what they look like to view in my living room.
Here are some samples. The first angel is actually a black. He really looks light black with pitch black stripes to the naked eye. The other angel is a silver and the stripes are much more prominent than appear in the photo. The others are just examples of how detailed you can get using the above methods. That koi sword is only 19 days old and TINY. You can make out the scale detail. The other sword is 8 weeks old and I was trying to detail the development of his sword on his tail. The betta is a cellophane and this photo accurately depicts the transparency of his tail.
Now, try not to spend all your time playing with your camera and remember that we cannot see too many photos once you get the hang of it
As far as your tanks go, love your ideas and all the input. That peppermint pleco is just adorable. I want one too.
I hope you succeed keeping cardinals with angels. I have seen photos of them together, great combo. Of course, cardinals look good with everything. I am a big fan of cories too. They are just so active. It would be a nice contrast to my more regal acting angels, but my tank can't take any more bioload. I have 12 in a 55g. I got them tiny. Didn't really expect them all to make it and am watching for signs of pairings and aggression. They are really getting big and I don't know if that tank can hold them all. I would recommend you choose your cories based on the color of your substrate. I have peppers on natural river rock. They look good, but the contrast of blacks would really look great. Another tank has black substrate with albino cories. They look the best.
Keep us posted. Its fun 'going through it' with someone else