I recently received an email from a reef aquarist that was concerned about her reef tank and sump setup.  The person was looking for a way to prevent siphon into her sump and thereby preventing flooding of her sump and display tank.  I wrote her back saying that I would right an article about preventing overflowing her sump and I gave her some tips on how to do such.

So how do you prevent your main tank from overflowing your sump in case of a power outage or some other saltwater tank catastrophe?  The short answer is simple.  Make sure that you leave enough space for saltwater in your sump in case your main tank siphons the water down into it.  So then what if your sump can not handle all the saltwater from your main tank? Then you have to get clever and figure out ways to break a siphon or to prevent the overflow.

 Let’s take my 46 gallon bowfront for example.  The main tank is 16″wide by 36″ long and when in a power outage my tank will loose 1″ of water due to a siphon before the water line hits my siphon break.  If my tank does not siphon break at 1″ below surface it will then loose 3″ of water.  Using the volume calculatorover at reefcentral.com I can predict that my 46 gallon tank will siphon down 2.5gallons of water into my 10gallon sump.  If It does not break at the 1″inch siphon line then the tank will siphon down 7.5 Gallons of water. 

My sump is only a 10gallon sump packed with equipment and the dimensions are 10″ wide, 20″ long and I keep it 5″ empty (meaning almost 3/4 full of water).  This allows me to have 4.3-4.5 gallons of siphoned tank water (from my 46gallon) before my sump overflows.

So if my siphon breaks are not cleaned correctly or if there happens to be a snail on each one during a power outage then I will flood my sump and about 3 gallons of saltwater will pour onto my floor and my wife will make me buy her new carpeting.  As improbable as it seems that two snails will cover my siphon breaks at the same time, it does happen.  This is why I keep 5″ of empty space in my sump, after all 3 gallons of saltwater is much better then 7.5 gallons when it comes to overflowing your tanks.

Pictured above is my 10 gallon sump, as you can see there is 5″ in the sump to cover for siphoned water.  The “Fill to here” sticker is so that my tank sitter knows how much water to replenish when I am away.

 Siphon breaks are just as important to Sump reefers as lighting is.  It is a protective measure that everyone running a sump should look into and use.  I created my siphon breaks on my 46gallon reef tank by drilling holes into my return line U tube under the water line right before the water from my sump is discharged into the tank. When the water level in the main tank drops due to a power faluire the holes in these tubes will start sucking air and break the siphon. 

The above and below pictures are of the U tubes that I drilled to create siphon breaks. Notice on the bottom picture that the siphon break is about an 1″ under water when the tank is filled.

Another method to preventing siphons are PVC check Valves.  These are great if your return lines are constructed of hard PVC pipes and if your handy enough for vinyl tubing as well.  They make these PVC check valves in many different sizes and threading.