Very nice shots
This is what I've learned about macros in general, & then trying to apply it to aquarium photography:
Piece 1: higher f stop = smaller aperature = broader field of focus. This is important when shooting a subject that occupies both a foreground & background. This is less important if your subject can be captured more or less "flat on", so to speak. But reducing the aperature has a trade off, which means letting in less light, which brings the next--
Piece 2: Shutter speed. Depending on your subject, you can get away with reducing the aperature & then slow down the shutter. Best for mostly static subjects, but not so good for a coral flowing in a current. Too slow & you could wind up with hot pixels, but this isn't so bad if your camera has a noise reduction mode.
Piece 3: ISO Speed. In a digital camera, this is only an emulation of film speed. Higher ISO rating is called a "fast" film, because the chemicals in the film react faster to the incoming light. On digital cameras, higher ISO tends to lead toward noisier images, though. The more light you're allowing into the camera, the lower an ISO you should use. If you have the aperature closed up pretty small & the shutter set pretty quick, then a higher ISO will make your camera more senstive to the reduced amount of light coming in.
Under my power compact hood, I find myself often shooting on ISO 400, an f stop of 5 to 7 or so, & anywhere between 1/8 to 1/60 shutter speed.
The long & the short of it is experiment like mad, get to know your camera, & get to know which areas & subjects in your tank need a higher or lower f stop, slower or faster shutter, & which ISO speeds are best depending on what lights are on. I usually don't like to use a flash, myself, unless I'm shooting a skittish fish, & in that case I usually just turn up the shutter to about 1/125 or so, & maybe bump the ISO down to 200.
One last bit, is try not to shoot an an angle through the glass (to the left or right, or too high or low to your subject), Try to shoot as straight through as possible. This will give you less distortion. The closer your subject is to the glass, the better!
Hope this helps!
