An overflow box is used when you are going to use a sump or a
refugium (depending upon setup) and your tank is not drilled or does not come with a built in overflow with a drain fitting. Now you can either drill a tank yourself, there are plenty of diy sites for drilling or you can have a glass shop drill it for you. Most large tanks, 70gal and up ,the bottom glass plate is usually tempered and is much more difficult to drill (however, most aqauriust will drill holes in what is to be the back of the tank). If a glass shop does your drilling - they as a rule will not cover the cost if the glass cracks when they drill it. An overflow box is used to take water from the tank into a box that hangs from the back of the tank (i attached a link that has a video clip) via a siphon setup of sometype and then has a drain at the bottom of the overflow box which can then be run down to the sump. Again some aqauriust have holes drilled and hard pipes setup (
PVC) to create a minifold so that intake and output are hidden, and other benifits. There numerous ways to get water from the tank to the sump - and it comes down to cost and preference - (however, if the tank is already setup and populated - then an overflow box is the way to go so you don't have to break it down for drilling - obviously) depending on the person - some people swear by overflow boxes, some people don't like using them. As you are doing read up on everything you can about setting up a
SW tank, because once you have setup, given the cost and the time - you have to live with what you have. Sorry to be so long in my answer.
[url="http://www.marinedepot.com/ps_ViewItem~action~view~idProduct~CR1511~idCategor y~FIOFEB~category~External_Boxes-Overflow_Box-Saltwater_Aquarium_Supplies~vendor~.html"]
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