Why have my aquarium plants stopped growing?

You wouldn't buy a bare-root rose and expect it to grow in a bucket of gravel, but this is precisely what many people do with aquarium plants. All plants need nutrients to grow and although biological processes will provide plenty of nitrogen in the aquarium, this is useless without elements such as iron. Being far simpler organisms, algae can thrive without many of the ingredients found in a good aquarium fertiliser so as strange as it sounds, adding plant food to your tank can be a great way of controlling algae growth by giving your plants a competitive edge.