Again, depending on the size of your sump, how deep in the tank the nozzle extends, and the size of your aquarium, this may or may not result in flooding. See also ReefBoxx is a New Affordable Battery Backup for DC Reef Gear Drill the returnĪnother potential drawback to HOB overflows is that if power is lost or the return pump fails, the return hose (through which water is pumped from the sump back to the display tank) can act as a reverse siphon, pulling water from the display tank down to the sump until the mouth of the nozzle finally catches air and breaks the siphon. Your dealer can advise you which pump is appropriate for your overflow.

Of course, you’ll also need to make sure the return pump is properly rated for the overflow system you’ve purchased so it doesn’t pump water back to the display tank faster or slower than the overflow can deliver it to the sump. If you have any doubt, get yourself a bigger sump! If your sump can’t accommodate all the water to that point, it will overflow onto your floor. In the event of a power or pump failure, water will continue to flow down to the sump until the level in the main tank drops below the slots in the internal chamber. They include: Choose the right sized sump and pump But if you do have an HOB overflow, there are some simple steps you can take to reduce this risk so you can rest easier whenever you’re out of the house, asleep, or otherwise unable to access the aquarium immediately. While this type of overflow can be a viable alternative to built-ins, it does have some possible drawbacks, not the least of which is the potential for flooding your fishroom in the event of a power outage, pump failure, or loss of siphon. The water then flows under the influence of gravity out the bottom of the external chamber, through a hose, and down into the sump, where it’s pumped back to the main tank through a return hose. Water is drawn from the inside chamber to the external chamber via a siphon tube (or sometimes more than one tube). In very simple terms, they consist of two chambers: a slotted box that is positioned inside the tank and skims water from the surface, and another box that hangs outside the tank. These overflows come in different designs, but they’re all more or less a variation on the same theme. Marine aquarium hobbyists whose tanks didn’t come with a built-in overflow or can’t be drilled to accommodate one (i.e., those made of tempered glass) sometimes choose to use a siphon-based hang-on-back (HOB) overflow to feed water from the aquarium to a sump.

Siphon overflow box