We stated earlier that, ideally, two types of water movement are necessary in an optimum reef tank: circulation through the aquarium and the filter, and current inside the tank itself.

Because of the nature of a reef tank and what is placed in it, areas with low water circulation are common. One such area is the entire back of the tank, behind the coral and base rock. Often the circulation in that area is low to non-acceptable because it is hard to create an even flow in such an area, unless the hobbyist designs it on purpose by using special water returns, or by placing power head pumps in the right locations. Indeed, rocks and coral base rock inhibits the even and continuous passage of water, and usually areas with very low water flow exist next to areas with good flow. Of course, as long as you are aware of it, and are willing to do something about it, this problem can easily be solved.

Several water return arrangements are possible, and we need to look at least at several of them:

6.3 AQUARIUMS WITH HOLES IN THE BOTTOM:

Whether to return the water to the tank through the bottom plate of the aquarium, by drilling holes through it, or whether to return the water from the top is a very personal decision. The advantages of returning the water from the bottom of the tank are that a better flow can be achieved easily, without sacrificing the outside view and esthetics of the aquarium. Indeed, returning it from the top makes hiding the pipe and hoses used to do so more difficult. But it can be done. The decision is entirely yours.

Drilling acrylic and plexiglass tanks is easy. All you need is a strong drill and some plastic hole saws. The size of the hole in the corner overflow box depends on the fitting you will use.

Get the fitting first, then decide on the size of the hole needed to pass that fitting through. A 1-1/4 fitting needs much more than a 1-1/8 hole. Drilling glass is not as easy, especially if you, or your local glass shop, do not have a glass drill. Best, usually, is to get the glass shop to acquire the tools, and volunteer to pay part of them if necessary. Mind you, they will have quite a bit of use out of them once they have them available, and you may be able to convince them to buy the required tools themselves. Check also with aquarium stores in your area. Some have glass drills, especially if they specialize in reef tanks, or have some experience with them. Determine whether your local aquarium society can be of any help.