This overflow box is generally considered a "weir" because it does not use a siphon tube but actually incorporates the whole width of the box as the siphon mechanism. This allows for more water flow and a less unobstructed pathway for the water so that debris and/or livestock cannot impede the siphon thereby causing a flooding situation.

The weir design is different for each tank configuration. In my particular case, I needed a weir that would lower the water level in the tank to below the crossbar that braced from the front to the back. This brace is constructed of 3/4" plywood that is mounted flush with the top edge of the tank, therefore lowering the possible water level to 1" so as not to allow the crossmember to be under the water level. You can see this crossmember in the picture of the third weir design to the right. Also note the vacuum tube attached to the side of the weir. This is a vacuum tube for an automatic shut-off switch for the return pump in case the tank level gets too high due to any unforseeable circumstances.


Taking this into consideration, I built the weir with the rear portion of the box about 6 inches deep and the front section about 4 inches deep (exact measurements are in the next section of this artivcle). The device can have almost any configuration as long as the rear section is at least an inch lower than the front section and the portion of the box that goes over the wall of the tank has adequate space for water flow, in this case 3/4 of an inch. Caution must be taken when designing the width of the overflow section because if the water is impeded there will not be sufficient flow to maintain a good siphon. I suggest at least 1/2 of an inch and not to exceed one inch.

These designs were adapted from a weir design by Melevs Reef online site. Note the tubing coming out of the top of both designs. These are to be attached to the venturi fitting on a Maxi-Jet 1200 to insure siphon continuance after a power outage and just to remove bubbles in general. This will be discussed in more detail later on in this article.

As a result I ended up building three of them. The first one was constructed from 1/4" acrylic, was 7 inches wide, and cost around $20. I failed to take into consideration the crossmember. It worked very well, but I had to fiddle with the height of the water flow so much that I did not feel that I was getting the full benefits of the design, so I decided to build another one with that in mind.

The second was constructed from 1/8" acrylite that I got from Home Depot for around $8, and was 9 inches wide (the extra inch in width would allow more water flow had I used a larger diameter bulkhead). This one worked very well as I had made the rear section 5.5 inches deep and the front 4.5. The flaw in this one was that I made the bend in the part going over the tank wall a little too narrow so that it fit too tightly and I had a leak in one of the parts of the design that is very hard to patch (more on that and some tips and tricks further on in this article).

The third one is the one that I am currently using and it also was constructed from 1/8" acrylite from HD. I lowered the rear portion to 6" and made the front deeper at 5.5" and made the unit 8 inches wide. The other flaws were taken into consideration and I have a weir that works very well. The bulkhead I used is a 1", and the flow is around 600-700 GPH. I am running a MAG 9.5 return pump flat out from the return section of the sump/fuge into the display tank, with about 3 feet of head.

The result is that I spent approxiamately $50 and ended up with the unit I am using now, a perfectly good backup unit, and one with a leak that is very fixable (pinhole leak) but that will need to be used on a tank with thinner walls.

This experience actually kind of stoked the fire for the rest of the AquascapeDS project. I had learned how to cut, drill, bend, glue, and in general work with acrylic.



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