SEMI-NATURAL: My 50-gallon Low-energy Fish Tank

Fish keeping is somewhat of a paradox--the hobby appeals largely to nature lovers, but the energy required to maintain an aquarium (with electric filters, lights, commercial fertilizers and water conditioners, etc.) is not exactly doing nature any good. And while many aquarists around the world have been successful with the low-tech "Natural Planted Tank" concept, I personally could not claim the same. So here's my answer to the dilemma: a fish tank that's designed to make the most of natural processes, with just a little help from modern technology.



From the very first time I encountered Diana Walstad's "NPT" (i.e., Natural Planted Tank) concept, I've had my sights on building one in my living room. In my opinion, it makes perfect sense--you get to have a vignette of nature in your home, without being an energy hog in the process (i.e., no need to run lights and electrical filters 24 hours a day; no need for commercially produced fertilizers; no need for frequent water changes).


But with a 20-gallon aquarium already in place (set up the traditional way, with laterite substrate, power filter and at one point supplemental carbon dioxide), space and cost limitations have gotten in the way. So, instead of wasting all the money I've invested in my 20-gallon tank and rebuilding it the Walstad way, I decided to use the tank as my personal NPT experimentation lab. Over the past eight months or so, I've been gradually introducing NPT elements into the aquarium and observing the results. So far, I've observed that most of Wastad's principles do, in fact, work; the only thing that hasn't seemed to work for me is the complete dependence on natural light (i.e., sunlight). In my 20-gallon tank, I've found that light-hungry plants (such as Rotala colorata and cabomba) do need at least a few hours of supplemental light a day in order to survive.

Such was how things had been until recently, when by some stroke of good luck, I came across an incredibly good deal and ended up with a slightly used 50-gallon tank with a metal stand, for about one-third of the regular price--and it even came with an interesting piece of driftwood and some 10 kilograms of white pebbles, free of charge! It was the perfect opportunity to finally get to build my own Walstad-style aquarium--only, considering what my recent experience has taught me so far, it will not be strictly an NPT, but more of a "semi-natural" tank. Here's how I went about setting it up:



Tank Concept
The basic idea is for this tank to depend largely on the natural symbiosis between fish and plants, with only minimal involvement from artificial contraptions (thus keeping energy consumption at a minimum). Water filtration will be done primarily by the plants--which consequently means that mechanical filtration should be minimal (if at all), so as to allow organic waste (like uneaten food, dead plant matter and fish feces) to be absorbed by the substrate, fertilizing it in the process. The sun will provide lighting, marginally supplemented by a low-wattage fluorescent lamp (4-6 hours a day). Aeration come from the plants, with some assistance from the bubbles produced by a 3-volt air pump (operated only at night, when plants are not producing oxygen). Activated carbon will be the filter medium of choice, for its water-purifying properties. Temperature control will not be an issue, thanks to the fact that I live in a tropical country.

Materials & Equipment:
All-glass 50-gallon tank (36" x 18" x 18") with metal stand
Substrate:
     generic garden soil (about 20 kilograms), purchased at a local garden supply shop
     leaf compost (one small bag), purchased at a local garden supply shop
     river sand (about 12 kilograms), purchased at a local pet store
     black sand (about 1 kilogram), purchased at a local pet store
     white pebbles (less than 1 kilogram), bundled with the glass tank and metal stand
Hardscape:
     rocks (assorted sizes, found lying around at a nearby construction site)
     driftwood (bundled with the glass tank and metal stand)
Other Equipment:
     low-power (3 watts), double-outlet air pump
     low-volume corner filter (with activated carbon granules and filter floss as media)
     standard 18-watt daylight flourescent lamp

Tank location
Considering the tank's semi-natural concept, the first major decision I had to make was where to place the aquarium; it would have to be a spot that receives some indirect sunlight--but not too much as to cause a drastic rise in water temperature. After much planning and consultation with my wife (who pretty much has the last say on anything home decor-related), I settled on the easternmost corner of the living room, next to a northeast-facing window. Here, the tank will be exposed to daylight from sun-up till sundown, with a portion of it receiving some 30 minutes of reflected sunlight when the sun is at a certain angle to the window.

Substrate and hardscaping
With the tank in its proper location, I was ready to lay the substrate. For this, I began with a base of generic river sand (to serve as a cushion and protect the tank's glass bottom from any sharp edges that the rocks and wood may have). A thin layer of leaf compost followed, which in turn was covered with a thick layer of plain garden soil.

Being a natural fertilizer, leaf compost eliminates the need for commercially manufactured solutions. However, I must note that if you plan to use compost in your substrate, bear in mind that compost, in general, tends to lower the PH of your water, making it acidic. And if you use regular potting compost (which contains animal manure), this effect can be magnified to the point of being harmful to anything but the hardiest fish. Thus, I recommend using compost that exclusively contains partially decomposed leaf matter. This, however, does not mean your water will stay PH-neutral; some acidity will still occur, but not enough to be harmful to your fish. The only down side to this is that using leaf compost can cause water tanning. Again, most commonly available aquarium fish are comfortable enough with this, but if you're bothered by the not-so-clear water, adding activated carbon to your filter medium is the easiest and most effective solution.

     

LEFT: Leaf compost over base of river sand (viewed from above and to the right of the tank).

RIGHT: Garden soil layer over leaf compost.

To top off my substrate, I used a combination of generic river sand, black sand and white pebbles. When using garden soil for substrate, it is important to use something heavier (and with larger grains) on top of the soil, in order to keep the latter from floating around and clouding the water in your aquarium.

For hardscaping, I used various-sized chunks of granite, and two pieces of driftwood. As with the location of the tank, my choice of hardscape layout was based on the objective of keeping energy consumption low. I had earlier decided that the focal point of my aquascape will be my red-leafed plants. And since these plants require lots of light, they would have to be: (1) closer to the water surface; and (2) at the spot where the morning sun would hit the tank. Thus, I created a mound in this general area, using the largest of my rocks and the smaller piece of driftwood as "dams" to help grade the soil. Furthermore, aside from the availability of light, I also considered the "golden rule" in choosing my focal point. In simple terms, this rule means placing the focal point off-center, approximately a third of the way from one end of the tank. And since my tank will be visible from two sides (from the front and from the right), I applied this rule on two dimensions: laterally (which places the focal point some 13.75 inches from the right end of the tank), and depth-wise (which puts the focal point at about 6.9 inches from the back wall of the tank).

With the substrate and hardscaping in place, I was ready to plant my aquatic flora.

My 50-gallon tank, ready for planting. Note the piece of tape at the bottom

of the tank (right of center), used to mark the focal point.

Plants

To take advantage of the varying amounts of light that this tank will receive, I selected plants with different light requirements--from low to high--to come up with an interesting and balanced aquascape. Below are the plants that I chose for this aquarium:

Plants that need high light:

     Rotala colorata

     Rotala rotundifalia

     Sunset Hygrophila (Hygrophila polysperma)

Plants that require low light:

     Cryptocoryne wendtii

     Anubias nana

Plants with flexible lighting needs:

     Sagittaria subulata

     Valisneria spiralis
     Amazon Sword (Echinodorus sp.)

     Water Sprite (Ceratopteris thalictroides)

As mentioned above, the plants with high lighting requirements went on and around the focal point, where they can receive reflected sunlight for about 30 minutes a day. Meanwhile, I planted Sagittaria subulata, Valisneria spiralis and Water Sprite on the sides and corners of the tank. From my experience with the 20-gallon tank, Water Sprite is a very invasive plant that can easily take over an entire tank if left unchecked. However, the species makes up for this bad habit by being an excellent water purifier. Thus, I consider Water Sprite to be a must for any planted tank--provided you trim it regularly, and cull if necessary.

To provide visual accents in the shaded areas of the tank, I tied some Anubias nana to the arch-shaped driftwood, and planted a few stems of Cryptocoryne wendtii underneath it. I also threw in a few bulbs of Red Tiger Lotus (Nymphaea zenkeri) deep in the most shaded part of the tank--over time, this will send leaves to the surface, where they will provide a nice pond-like look. On the other end of the tank, I planted an Amazon Sword. Next to it, I placed a stem of what seems to be Dwarf White-stripe Bamboo (Pleioblastus fortunei), which was donated by a supportive friend. I'm hoping this plant will grow to well above the water surface and provide a unique accent to the tank. For now, however, the top leaves are just barely reaching the upper edge of the tank, and I have yet to see if the plant will actually grow any taller.

Equipment

With the plants in place, I proceeded to install my tank's "tech aids". On the least conspicuous corner, I placed a small airstone-powered corner filter, filled with activated carbon granules and a thin sheet of filter floss. On the back wall, I placed a spray bar. Both of these were hooked up to a twin-outlet air pump, which when turned on will cause enough bubbles to create significant surface agitation and gas exchange--and give the aquascape a nice, dynamic backdrop as well. Above the tank, I installed an off-the-rack lighting assembly with a 6500-Kelvin,14-watt T5 fluorescent lamp, positioned to favor my red-leafed plants. I placed aluminum foil on the inner surface of the lighting hood, to help increase the intensity of the light without consuming additional power. I,m hoping that this, combined with sunlight from the window, will be enough for my plants' needs.

Fish Stock

With everything in place, it was time to fill the tank with water and introduce my starter fish. After filling the tank to just below the topmost leaves of the Dwarf White-stripe Bamboo, I gently netted my school of four Zebra Danios from my 20-gallon tank, and placed them in the new tank. Being hardy and tolerant of a wide range of water conditions, Zebra Danios are among the most popular starter fish, and are commonly  used to cycle a fish tank. Since most of my aquatic flora were transplanted from established tanks, I presumed that the plants were already teeming with nitrifying bacteria, thus shortening the cycling period. The rest of the fish from my 20-gallon tank (comprising three Rosy Barbs, two Red-eye Tetras, one Blackskirt Tetra and one Red Serpa), will be transfered gradually, about two heads per week.

Newly completed set-up, with initial stock of four Zebra Danios and a few snails. 

The reddish hue of the light is flattering to the colors of the fish, but is not very beneficial for plants; thus, I eventually switched to white light.

With the set-up complete, I now have a moderately large fish tank designed to sustain a community of tropical fish at a fraction of the energy needed to run a more traditional set-up. Once fully cycled, this tank will have artificial aeration only at night (when plants are not producing oxygen), and have artificial lighting for only 4-6 hours a day. Mechanical filtration will be minimal; instead, fish waste and other organic matter will be allowed to settle on the substrate and eventually fertilize the plants. The combination of submerged (i.e., completely underwater) and emmersed (i.e., with leaves above water) plants will provide water purification and oxygenation, with only marginal help from the air pump. Water changes will be done bi-weekly, if not monthly (other NPT owners have reported going several months without water changes).

Night shot of my tank, 2 weeks after set-up, with additional fish stock and white light.

Post Script

For all the rationalization that went into almost every aspect of this tank, ultimately it is still an experiment, and only time will tell if everything will actually work as planned. Along the way, I'm quite sure that I'll be making several adjustments to the set-up. Nevertheless, it gives me a certain sense of fulfillment to know that I can enjoy this enchanting hobby without severely increasing my carbon footprint.