i actually find you can get better quality closeups if you sit away from the object (or stand, or lay down) and use the zoom - assuming you have a good enough zoom

my fuji S5700 has done some great pics that way
using the zoom, in macro mode, will do nothing but give you un sharp pictures. using the zoom without macro, results in the same. simply, as you zoom the lens, the minimum focusing distance increases. it may work with the digital zoom, don't know i have never switched mine on!!! and would never use it. if you add the fact that most "zooms" on low/mid end compacts, aren't actually zooms at all, but are Veri focal ( i suggest google for finding out the difference, it would take too much space up here)
dont get me wrong, i'm sure you get great pictures. but unless you have a, really bad macro setting, I feel, you could improve on your pictures using macro properly.
i actually find you can get better quality closeups if you sit away from the object (or stand, or lay down) and use the zoom - assuming you have a good enough zoom

my fuji S5700 has done some great pics that way
Great idea yes!
Also, my old Nikon 8700 required that I had my zoom at a specific point to get the best out of macro so a read of the instructions is a good idea at this point!
it is well worth a look at the instructions, if nothing else it will tell you the cameras focusing range, in macro, usually something like 2-30cm or so.
low light, as stated, is often the cause of "bad" fish pics. it forces the camera to use a more sensitive ISO/ASA, with a cosponsoring loss of quality. added to that the shutter speed is often low (camera shake) and the lens is "wide open"( set to its maximum light transmission) which is where it is producing its worst results.
you get three basic choices when you want to take pictures of fish:
1, natural light (ambient)
2, artificial light (ambient or specific)
3, flash
in an ideal world, flash would be the best option. it freezes the action, allows a smaller aperture, and lets you use a lower (less sensitive) ISO/ASA. but we take pictures through glass, of fish in water. all these things cause problems and changes to the light that reaches the camera. that main argument against flash pictures of fish, when you can get a good one, is that they look a little unnatural. this can be fixed in Photoshop or the like, but you really need to know your stuff.
daylight would also seem to be a good option. if your tank is in "good" daylight, hanging some net curtains will help diffuse the light(helping to avoid unwanted reflections) if you can obtain shutter speeds that avoid camera shake, you should find you get good results.
ultimately, artificial light (those in the tank and room) is what many have to use. it is often said that removing room lighting and using only the lights in the tank is the best option, and i agree. ambient light from the house lights will, almost always, cause unwanted reflections. and it will have very little effect on the pictures, as the lights within the tank will be stronger..
for myself i add an extra light I bar, and old rio one i have hanging around, then i close all the curtains and switch off the room lights. i use a tripod occasionally, but more often than not i hand hold. i do have a really useful mini tripod (local £1 shop). his allows me to rest the camera, either on the glass or the stand, making close up pics much more manageable. as for camera settings, i set macro, switch off the flash and set 100ASA/ISO. i leave the exposure to the camera, but i do set the "white balance" to fluorescent. (this helps less than you would think, as the light from most fish lights does not conform to the FLD balance set by the camera) after that its just a case of practice. getting to know your camera and modifying your technique as you learn.