If you have both an aquarium and a garden (or just a few houseplants) you should consider using the waste water from the aquarium on your plants. In addition to fish wastes and decaying fish food particles, the water also contains helpful bacteria and trace nutrients that can help your plants thrive.
Photo by Victor Martinez
The author of gardening weblog Dave's Garden says that after applying waste from his 55-gallon aquarium to his flowerbed, it outperformed the prior flowerbed by 200 per cent. He also points out that if you lose fish you should dig them into your garden soil rather than flushing them away for even more natural fertiliser.
Aquarium Water - Liquid Gold for Your Garden [Dave's Garden]