CountryLovah, u might wanna check this link for inspiration:
Those are the winners of Creative Display Tank Competition in Singapore a few years ago.
Might I also suggest sticking to a coherent theme and not laden the tank with ornaments? Maybe one or two complementing pieces of decor as focus points but don't put just anything & everything in there.
Think about the colours also. Better to choose a main colour theme then using different hues of that colour rather than many mish-mash of colours.
Less is more, so they say