It's not a bad camera considering it came out 4 years ago, dpreview gave it pretty high marks.
http://www.dpreview.com/reviews/olympuse510/page31.asp. They say it does get noisy above 400 ISO, so you aren't going to be able to push your ISO very high. It is a micro 4/3 camera, so lens selection is not going to be nearly as extensive as if you had a Nikon or Canon with an APS-C or Full frame sensor. That said, you will eventually want a faster lens, one that goes down to 2.8 or below on the aperture, especially since your camera doesn't do so well above 400 ISO. Before you go out and spend many hundreds or thousands of dollars on lenses, you need to decide if you are going to stick with the 4/3 format. If you do decide to stick with the 4/3 format, there are newer cameras with better low light performance, but you are still stuck with the lens availability problem.
Before you start doing all that research and making those decisions, you can still take good pics of your aquarium with the camera you have. Use your biggest zoom lens and set up a little farther away, but zoom in to what you want to take a pic of. Try using the flash with the camera pointed at an angle to the glass to avoid reflections. Use the tripod and the delay timer to avoid camera shake, (just pressing the shutter button will cause the camera to shake), or, even better, a remote shutter release. Don't worry too much about white balance, you can usually fix that in post processing (photoshop).