Hi, this is Ashlee from Pet Planet in Riverton, Utah. I'm here to show you how to set up an in-tank heater. One thing that you want to make sure you do is you want to make sure that when you get it out and you first put it in your tank, before you turn it on, you need it to sit for at least a half hour. If you don't, it won't adjust properly to the temperatures. And also, before you take out your heater, make sure it's been off for about a half hour, that way, it will avoid any shatter of the glass or hot/cold. It's just a precaution. First of all, if you are setting up a tank just for a goldfish, just keep in mind you do not necessarily need a heater for a goldfish. Other fish that you will need a heater for would be tetras, very...more sensitive fish, loaches, and sharks.