If you can, post a photo of something you've taken with the settings you have so far. I think that'll give everyone a better idea of what problems you're having.
FWIW, that camera does have a macro function. On the Sony's its usually designated by a little flower icon. Press that and then take the photo. That should get you started. Also, try turning off the flash which is the little lightning bolt icon. Keep pressing it until you see the ghostbusters "slash-through" symbol over it. Then try taking another photo. Practice shooting at something that isn't moving inside of your tank. You can also try increasing the ISO and maybe even shooting in sports mode. Unfortunately, your camera doesn't have shutter priority (the ability to manually change the shutter speed) so sports mode might be your next best bet. HTH.