I have had a freshwater tank for about 6 months now and I have had my saltwater tank for aboutu 2 months now. I have been looking on this website and I have found that a lot of people have pipes going from their main aquaiam to a smaller aquarium called a sump. What is this used for? Is it helpful? Should all aquariums have it? Thanks!

This will help...

http://saltaquarium.about.com/cs/bcorse ... 8sumps.htm