A River Runs Through It 

The allure of a river. The splash and glistening of a waterfall. What is it about the flow of water that is so appealing? Perhaps it recalls a more primitive time, where the fresh water we drank was best found in a babbling brook. This primitive quality, the lushness, the natural beauty of a stream cutting its way through the granite rock face of a mountain, that was the scene that I wanted to recreate in my ‘river tank’. 
Having built a few outdoor ponds with streams and waterfalls, I thought that a terrarium with the sound of tumbling water coupled with lush plant growth would make for an interesting display. However, I had always used heavy black plastic for pond and stream construction, and in this case I wanted to use only ‘natural’ building materials. The reason was simple: the size of the system was to be much smaller (a 75 gal aquarium versus a pond system with thousands of gallons), and the observer would view the display from up close. To create the effect of a totally natural system, no plumbing or man-made materials were to be visible.  

Drawing also from a little experience with terrarium type setups, coupled with general tinkering in the construction of filters for aquaria, I had a general idea of how to build a River Tank. Oddly, my main goal was to eliminate as much maintenance as possible. I wanted a totally self-sufficient tank. No filter cleaning, watering plants, feeding fish, or cleaning of any kind. I wanted the system to be self-contained, so that it would run unchecked for months on end. This seemed to be a tall order, but I thought it would be possible given the type of aquaria being employed. With a terrarium, it would be possible to balance the needs of the fish with the needs of the plants. The water would be the transport system. The plants would use the nutrient byproducts of the aquatic life. The only inputs for the system would be light and water, and both could be provided automatically.  

Most importantly, the system was to be an interesting display. I wanted the maximum use of the space provided in the 75 gallon aquarium. There would need to be a balance between the plants and the water. The massive amount of stone needed to create the superstructure would be softened by the plants. The idea was to create a natural looking system, and allow it to function in a natural way.  

Pre Construction  

The all glass aquarium was the base of the display. It would have been nice to have only as much glass as was needed to hold the display in place, but custom building the aquarium would have been difficult. And I was trying to use an existing empty aquarium. However, I did think that I could minimize the effect of ‘seeing’ the glass, by removing the top trim. The trim was made of plastic and was glued in place with silicon sealant. By cutting and removing the trim, and then removing all the remaining silicon, the glass would tend to disappear and let the viewer see directly into the tank. I imagine this trim added some structural stability to the aquarium, but as I was not going to fill the aquarium with water, I did not see the harm in removing the trim. 

In building the river habitat, the primary consideration had to be for the well being of the plants. The plants were to be the main focus of the tank, and thus it was important that they should exhibit lush growth. Thus, decisions regarding the composition and design of the tank were restricted by the needs of the plants. For example, the area for the plants had to be above the water line. Space was made for the planting areas. These areas were located behind the pools of water to allow the plants to grow out over the pools. The pools were to be constructed out of rock. Therefore, many rocks of varying size had to be obtained, washed and dried before construction could commence. 

Placing the plants well above the water line would prevent their roots from sitting in water (which could induce root rot). But, I wanted to give the plants access to a constant supply of water, thus eliminating the need to water the plants individually by hand. The planting areas needed to be filled with a material that would allow the plants to send roots down to the permanent water level. Since the pockets in which the plants would grow had no bottoms, large rocks were used to fill the space. Next, smaller rocks were used, followed finally by gravel (.1-.4 inches). On top of the gravel, potting soil was added, and the plants were planted in this medium. As it turned out, initially, the plants had to be hand watered, but within a few weeks, the plants had extended their roots to the bottom of the aquarium and a constant water supply. The plants never needed watering after that point.  

The system was located in a poorly lit room in the basement. Thus artificial lighting was required. The idea was to spot light the tank while not illuminating the entire room. Incandescent spot lights were chosen due to their availability and low cost. Four 65 watt spot lights were used. Plants had to be chosen which could grow in the low light levels. Tropical plants turned out to be the perfect choice. 
Some small fish would be added to give movement to the display, as well as provide for a source of nutrients. These fish would need to be able to survive on limited resources, as feeding was not part of the maintenance regiment. Gold fish were eventually selected, and proved to be quite able to survive with out adding food to the tank. 

An additional consideration was to keep the water in the terrarium as clean and clear as possible. The display would be much less appealing if the water was green, or if the rocks were always coated with algae. Also, some under water plants would be added. To help filter the water I decided to add a small “swamp” in an empty area in the front left corner of the aquarium. The dirt for the swamp area came from a back yard swamp which was the filter for a pond system (see FAMA Feb 1996 “Swamp Filter-A Revolution in Pond Keeping”). In addition, rinsed dirt (sand) from the backyard swamp was added to the bottom of the aquarium to give the plants a growing medium, as well as to provide habitat for microorganisms and have an area for additional nutrient recycling.  

Carbon dioxide was a concern for the underwater plants. However, as the tank was to have several small waterfalls, the flow of water from one pool to the next would help to introduce atmospheric carbon dioxide.

Diagram 1

 
Readily abundant field stone (granite) was used to divide the tank into sections. The idea was not to plan the outcome, but to let the shape of the rocks dictate how the tank should look. The result was four pools of water, each higher than the next. The lower pool was simply the base of the aquarium. The bottom water level would be around five inches. A small power head located in the back right corner of the tank was connected to a piece of pvc pipe which fed water to the highest pool (see Diagram 1). The water height in this pool was about two inches from the top of the aquarium.  
After the field stone was set in place, smaller stones were used to line all sides of the water works. All stones were cemented into place with clear silicon sealant. The larger stones were heavy, and once put in place, did not tend to move around. For the waterfalls to work properly, each pool had to be fairly leak proof. Once the tank was full of field stone, smaller rocks were placed in a manner to create a bottom for the pools. Lavish amounts of clear silicon sealant was used to cement the rocks together and allow the pools to hold water. When building the bottom of the pools, as large a rock as possible should be used, as if you were adding a large piece to a jigsaw puzzle. The final stage is to use small rocks to hide the silicon joints. Small rocks were simply given a dab of silicon, then placed on top of the silicon joints. The end result was a very natural looking all-rock landscape with no silicon showing. 
After all the rock had been put in place, the system was repeatedly tested for leaks. The pools needed to hold water so that the water would flow over the falls, and not simply leak through the bottom of the pool. The pump and hose needed to be connected, and the heater placed in its location behind the rock wall. From the top pool, the water ran over the first waterfall into the second pool. In this manner, the water proceeded through the next two pools and over waterfalls until it reached the bottom pool, and was re-circulated by the pump. An estimated 25 gallons was in circulation. Once the water works were working properly, all that was left was to fill the area where the plants would be housed as described above.
 
Flora and Function  

Shade tolerant plants were used due to the lack of natural lighting, and to avoid having to use high powered metal halide lights. Tropical plants worked well as the room and tank were heated. Vines such as a velvet leafed Philodendron were added, and eventually they ran all over the aquarium (and the walls). The plants, soon after being put in place, sent runner roots which reached the bottom of the aquarium and the permanent water source. The nutrients supplied by the few fish and the constant water supply led to lush growth. All in all, the plants outdid all expectations. The Maidenhair fern was exceptionally lush, especially for a very fussy plant. A few plants did not like the dim light and wet conditions, and did not do as well. They were removed. Eventually, the remaining plants grew so thick, they seemed to overshadow the river environment. But the echoing sound of water splashing down over three waterfalls immediately brings the flowing water into focus.  

System Support 

The most common form of maintenance for any aquarium is the ubiquitous fresh water top off. This could be a real chore for an aquarium where water was flowing over waterfalls and where hot incandescent spot lamps were used. Evaporation was sure to be high, higher still during the dry winter months. So an automatic watering system was added. It consisted of a kitchen sized garbage can, a float valve, and some tubing. Water was connected to a Reverse Osmosis unit using 1/8th inch tubing. This connected through the side of the trashcan and into an inexpensive float valve (much like a toilet float valve). Airline tubing ran from the bottom of the trashcan to the bottom of the aquarium. The trashcan was set at the proper height to maintain the correct water height in the aquarium. For two years, this system has supplied water to the tank every day with no maintenance.  

Conclusion 

Terrarium keeping is a branch of the hobby where we can explore the underwater world as well as the terrestrial world, and see how these worlds interact. The system is simple in design, tolerant of extreme conditions, and requires very little maintenance. It might be said that keeping a terrarium is easier than either keeping house plants or a simple gold fish tank, because the interaction of the terrestrial and the aquarian realms helps to balance the system as a whole. The allure of a lush terrarium system can be enhanced with the simple movement of water. With the myriad of small submersible pumps available in the hobby, adding the sound of dripping of running water is a logical next step.  

Pictures 
The system 
The completed system Build photos 
Water replacement only needed: where the plants were watered automatically, the water was kept clean by the plants, the fish in the system provided the nutrients for the plants...This would require three things: water, adequate lighting and fertilizer. To reduce maintenance, the plants would need to receive all three requirements automatically. Lighting would be easy to supply, and a timer would regulate the photo period. The plants would receive the necessary nutrients from the waste products of the fish. And water would be supplied automatically by a float valve.