If you want to keep goldfish and guppies, I highly suggest getting a tank as a kit...Tanks sold as kits are targeted for beginners because "everything" you need comes with it. However, the heaters are usually hang on ones, which totally blow... The filters are rated for the tank, but most hang on the back filter companies over rate their filters, so you will want to get a bigger filter. If you just want to keep a few tetras and some simple fish, a kit will be fine. If you want to expand your choices of fish both species and quanity you can safely add, buy everything seperate. I suggest buying fiters and heaters online. You will pay about $8 to ship, but you will save that on a heater alone. I have been using Drsfostersmith.com for over 10 years and like them. Others, however, like BigAls and other online stores. If you do not want to do that, try looking on craigslist online. You can usually pick up a lightly used setup for a fraction of what you would spend on a new set up. Hope this helps.