It may be fun purchasing up all sorts of inexpensive aquarium livestock when first setting everything up, but keep in mind what these purchases will be like a year or more down the road. For example, damselfish are very popular among new aquarists. They are very hardy, and are often quite colorful and entertaining to watch. Unfortunately, they can essentially turn into demons of your aquarium, bullying other fish and killing more expensive and delicate animals. For new coral keepers, Anthelia and Kenya Trees are often purchased. These are usually very, very cheap (sometimes free) and they grow like crazy. This is a welcome site to the new coral keeper, but in a few months time, these corals can dominate a display and be a pain to remove once the hobbyist develops a taste for other types of coral. So, with every purchase, consider how the animal will be in the future.