Fish keeping is a very addictive hobby. Anyone in this hobby knows multi-tank syndrome and "suffers" from it. After many years in the fish keeping business I decided not to buy (yet another) tank, but to venture into something unique that I am sure nobody or very few people in the world have tried. This concept was an aquarium water-bridge and I decided to go ahead and build one. This turned out to be my most exciting project ever in the fish keeping business and it has entertained my family and me for years, as well as visitors who have come to see it. What is an aquarium water-bridge? An aquarium water-bridge is a clear tunnel of water that travels above the water line between two aquariums in which all or most of the inhabitants of the tanks can swim. Imagine two 4 foot tanks standing 3 feet apart, and fish swimming out of one tank, and into the other. Even more absurd, imagine that they swim almost a foot above the water line, as if they had wings and enter the other tank, a completely different environment. How does the water-bridge work? The water-bridge is based on the same mechanics that keeps water in a bottle when it is raised out of the water in an upside down position. If you fill a bottle with water and and raise it (upside down) out of a tub of water, no air can enter the bottle and therefore no water can escape from the bottle: hence all the water remains in the bottle. You can almost raise the bottle out of the water completely before it catches air and the water runs out. The water-bridge uses the same mechanism to keep the water inside the tunnel, except that there are two openings, neither of which allows air inside. One opening is in tank A, and the other opening is in tank B. Was it worth the effort? Yes. No let me repeat that: yes, yes and yes! Almost within 20 seconds of loading the bridge, my Siamese Fighter swam inside. He hesitated for a while then he returned into the original tank. He then became totally inquisitive and decided to enter again. This time he swam to the other side and "Hey Presto!", entered a brand new environment. From then on he spent 80% of his time in the water-bridge leaving the bridge only on occasions to breath air on the surface of the 2 tanks. He almost claimed the bridge for himself, like a troll! On a regular basis we had pearl gouramis and other gouramis, plecs, angelfish, rainbowfish, red finned sharks, swords and tetras swimming through. Fish that did not enter were silver dollars, some loaches and certain types of sharks. What made the water bridge spectacular, is that it sometimes amplified the image of the fish when they swam through. This was remarkably spectacular with the pearl gouramis. The pearl seemed at least 3 times its normal size when it swam closely to the edge of the tunnel and it emphasized the brilliance of this already beautiful fish. Then there was a male freshwater lobster that claimed the one side while the female lobster claimed the other side. All one could see was their feelers and pincers sticking out into the tunnel, sleeping there in total bliss. The lobsters often crossed the tunnel 4 or 5 times a day. A lobster molted in there on one occasion and we watched as he undressed in the magnified tunnel. Incredible! The Siamese fighter and a female even spawned in the tunnel on another occasion. And the apple snails loved to cross the bridge regularly. All the inhabitants somehow instinctively knew the bridge was there and how to use it. Are there any advantages besides the uniqueness? Yes, there is more water in each tank, so the water is more stable. It is like having one 8 foot tank. The fish seem happier as they constantly explore between the 2 "changing" environments. Breeding pairs are naturally separated for days, giving the female time to recover, and seems to trigger the spawning process when they meet without the stress of human intervention. The tanks are also easier to move than one 8 foot tank. How was it built? It was very easy to build. You can very easily build one yourself in less than 2 - 3 hours. The most difficult material/part to find is the clear tunnel piping. I used 110mm clear PVC piping. This almost looks like glass and to the untrained eye looks exactly like glass. It was quite expensive: 400 ZAR ($50), but that is mainly because it is imported. For the bends I used 2 normal white 90 degree 110mm PVC elbows. I also extended the vertical ends with a small length of standard white 110mm piping and glued a PVC threaded terminator on the end for a normal white 110mm PVC screw on cap. This would become useful when loading the bridge. The PVC pipes are simply forced into the elbows. I used the elbows with the rubber rings that requires no adhesive to be applied. The most work is required to build the brackets that hold the water-bridge on top of the aquarium. I used a piece of flat bar aluminium and bent it into 4 legs. These legs would stand on the top of the aquarium support glass that holds the top edges of glass (of the aquarium) together. I would not rest the bridge on the sides of the aquarium glass as the bridge is rather heavy. I used 4 aluminium brackets that are commercially used to support 110mm piping. There brackets were riveted to my 4 aluminium legs, and thick rubber pads were stuck to the bottom of the legs so that they would not scratch the glass. You will need 2 brackets on each side of the tunnel between the bend and the clear PVC tunnel. Ideally I would have liked to use clear PVC elbows but I could not source these anywhere. It is not recommended to use a smaller diameter than 110mm for tropical fish. All fish should comfortably fit through the water bridge. It is also possible to go for 150mm or 200mm; however, these would probably be too heavy for the aquarium glass and would need to be supported on a wall. How do you get the water up there? This is a question that I was always asked by first time visitors. I often said " I place my head under water and suck on the one end." And it makes them even more inquisitive. Getting the water up there is very simple. You turn the water bridge upside down so that the openings are facing upwards. Preferably outside, and fill the bridge, until there is no air in the tunnel or in the elbows or extensions. Do not forget the anti-chlorine. You then screw on the end caps allowing as little air as possible to be trapped in the extension pipes and tunnel. When both caps are secure, you can go inside and at the very last minute, flip the bridge around that both of the entrances are under water. Unscrew the caps that are now under water. What happens if the water level drops below the entrance of the tunnel? The obvious. Water runs out of the water-bridge in both directions and floods your lounge with the content of the water-bridge. I have never allowed the water level to drop to lower than 1 inch from the threaded opening of the bridge. Do the fish get stuck up there? Yes, if there are lobsters on either side that do not allow the fish to escape. This happened once and the fish waited in the middle of the bridge until one of the lobsters decided to leave the bridge and enter the tank again. The fish was not stressed. But in all other cases, the fish seem to instinctively understand. Up = In. Down = Out. Does the water not stagnate up there? No. I pump water out of my one tank through an external canister filter and into the other tank. Gravity keeps the water level of the two tanks the same and there is constant motion of water through the tunnel. It also keeps the chemistry of the water in both tanks the same. If your filter pumps 2000 liters of water an hour; this is the volume of water that passes through the bridge every hour. Does the water-bridge clog up with algae and debris? Surprisingly not. I expected to constantly have to clean the tunnel of algae and other dirt. The bridge has been running for a couple of years, and I never needed to clean it. I suppose the plec and the apple snails helped to keep it clean. Cleaning would be easy. You just fill the tunnel with 50% water and then shake it until it is clean. You can also use a magnet like you clean your aquarium glass. But be careful:- PVC scratches very easily. What does all of this prove? Fish keeping is seriously interesting and a fish will swim almost anywhere where there is water.