The settings for a full tank shot are going to be different than macro shots generally speaking. You can't say "these are the best settings... use them" because you have to decide how you want the picture to look; the settings will change according to what you have in mind. A beginner will just take what the camera gives him in auto mode, and hope it looks good. Someone familiar with how a camera works will be able to decide how the picture would look ideally, and make the appropriate adjustments to the aperture, shutter speed and iso. Of course, you don't always get what you want
Photography is a game of compromise, especially in harshly lit reef tanks- aquarium photography can be really tough- glass, water and harsh light... add up to tough.
Anyways- the best thing to do is learn how the camera works and practice, so you can see how the different settings make the shots look different. The first/oldest article on
this page will teach you the basics, with some examples of pictures taken with different settings. The newest article has some specific tips that will hopefully help you even more.
It seems like a lot to learn at first but it's not too difficult once you learn how shutter speed and aperture work together.
Posting pictures for critique can be a good way to learn too.
Hope this helps,
Greg