OK, at first I thought you were talking about a tablet or cell phone, but I guess Samsung now has an actual camera called the Galaxy. First off, I think you're still going to be far more successful with your DSLR. It's not all about the megapixels. The size/quality of the sensor and the quality of the lens are far more important. That said, if you choose to still use a P&S camera, with the settings you have available, it's really going to be the same considerations as a DSLR. If I'm shooting moving subjects, my first concern is setting a fast enough shutter speed to capture the action, followed by aperture to give me sufficient depth of field, sacrificing that as necessary if it's going to drive my ISO too high. For non-moving subjects, my first concern is setting the aperture for the correct depth of field. Assuming you're using a tripod, you can then keep the ISO nice and low and adjust the shutter speed as required for the exposure.
All of this takes practice as well as an understanding of how shutter speed, aperture and ISO affect your final product. I hesitate to try to give you any sort of all purpose setting, because at that point you may as well just throw the camera into auto mode. There are simply too many variables that I cannot predict for your tank.
