LAYOUT vol.007

English version of this article originally published in
Tropical Fish Hobbyist Magazine.

Lighting and CO2 in the Nature Aquarium

Nature Aquarium is a layout style developed for growing healthy aquatic plants and creating a beautiful aquascape over a period of time. Therefore not only the skill to produce a layout is required, but also the skill to nurture aquatic plants. Since the systems to grow aquatic plants are well established these days, we can prepare a good growing environment for aquatic plants by using appropriate equipment. In this issue, I am going to talk about the two most important systems for growing aquatic plants: lighting and CO2 injection.

Aquatic plants grow by performing photosynthesis. It is well known that photosynthesis requires light. However, light-loving plants that perform photosynthesis vigorously and shade-loving plants that do not perform photosynthesis quite as vigorously require different amounts of light. I am going to discuss mainly the growing environment for light-loving plants since growing light-loving plants tend to produce more issues in an aquatic plant layout.

An Iwagumi layout of Nature Aquarium is often planted with relatively short aquatic plants. Glossostigma, Riccia and Hairgrass are representative of these. These plants are light-loving plants that require bright light for growth. Therefore they need to be provided with the brightest environment possible. More specifically, these plants in the 180 cm aquarium in Photograph 1 are grown under three 150W metal halide lamps. Since metal halide lamps are very bright, only three lamps are needed. If fluorescent bulbs were used, twenty-four 20W lamps would be needed. With that many fluorescent light bulbs, the entire top surface of the aquarium would be covered with lighting equipment. Six 32W fluorescent light bulbs that are used for the 90 cm aquarium in Photograph 3 cover up the top of the aquarium. In Nature Aquarium, pendant-type metal halide lamp fixtures are gradually replacing conventional light fixtures for the open feeling and ease of maintenance. One 150W metal halide lamp provides sufficient brightness for a 90 cm aquarium.

Without a sufficiently bright environment, light-loving aquatic plants cannot photosynthesize vigorously, and their growth will be limited as a result. Since the light energy becomes rapidly attenuated in water, we must be watchful about the light condition especially in a tall large aquarium. If the brightness of the lighting is not adequate, Riccia and Hairgrass do not grow much at all and Glossostigma tend to grow runners vertically. When these symptoms show up, the first thing to be questioned is the amount of light. In an adequately bright environment, Riccia produces air bubbles at the tip of its leaves and Hairgrass and Glossostigma grow by sending runners sideways.

Although fluorescent light and metal halide lamps come in various types, full spectrum lamps high in blue wavelength are utilized in Nature Aquarium. Blue spectrum is highly transmissive in water and therefore more suitable for encouraging aquatic plants to photosynthesize vigorously. However, since the image produced in blue light alone looks like a deep-sea picture, red and green spectrums are added for balance so that aquatic plants and tropical fish look more attractive. In an aquatic plant layout, the bright light is not the only thing required for vigorous photosynthesis. In an aquarium with a limited amount of water, CO2 within the water is rapidly absorbed and becomes depleted in a short period of time when aquatic plants start photosynthesizing. CO2 is essential for photosynthesis. If CO2 is depleted, aquatic plants stop photosynthesizing. If aquatic plants are not photosynthesizing adequately in a bright environment, you should suspect a CO2 shortage. You can confirm the lack of CO2 by testing the water since pH rises rapidly as CO2 starts to run out.

CO2 injection is essential if you wish to grow a lot of aquatic plants in an aquarium as in Nature Aquarium. This is especially true if you use light-loving plants that photosynthesize vigorously. Although there are many ways to inject CO2 in water, Nature Aquarium utilizes the natural injection system in which CO2 is diffused into the water column as fine bubbles through a sintered glass diffuser. In this injection system, a high-pressure liquid carbon dioxide gas cylinder is fitted with a CO2 regulator and CO2 gas is brought to the aquarium with a tube. The amount of CO2 injection is checked with a CO2 bubble counter and adjusted with a needle valve (Photograph 5). Different size diffusers are selected depending on aquarium sizes. The larger the aquarium, the larger the diffuser becomes.

An important thing to keep in mind when injecting CO2 to an aquatic plant layout is that the amount of CO2 needs to be adjusted according to the type and the amount of aquatic plants and the rate of their growth. Once you gain enough experience, you will be able to judge the proper CO2 level through the photosynthesizing condition of aquatic plants and the leg movements of Yamato Numa Ebi (Caridina japonica). In an adequately bright environment, light-demanding plants such as Riccia, Glossostigma and other stem plants actively perform photosynthesis with an increased CO2 concentration. However, excessive CO2 affects fish and shrimp adversely. Therefore a proper CO2 level should be the level that aquatic plants can adequately perform photosynthesis without being detrimental to fish and shrimp at the same time. Yamato Numa Ebi is sensitive to the increase of CO2 concentration. As the CO2 concentration increases, their leg movement becomes slow.

It is safer initially to judge if the CO2 concentration is appropriate or not by measuring changes in pH. When CO2 is added to water, pH level decreases. As CO2 is consumed by the photosynthesis of aquatic plants, the pH value rises. Provided that the water quality of the original water is neutral (near pH 7.0), if the water becomes slightly acidic (pH 6.8 to 6.6) with CO2 injection while aquatic plants are vigorously photosynthesizing, you can consider the CO2 level is adequate. I hope you can now grow healthy aquatic plants by maintaining a proper CO2 level.

ADA’s pendant style lighting fixture "Solar I" Since a bright metal halide lamp allows the light fixture to be suspended high above the water surface, you can create an open top aquarium resplendent with airiness.

Nature Aquarium CO2 injection system measures CO2 injection volume with a glass counter and diffuses CO2 into water as fine bubbles via a sintered glass diffuser. (ADA’s CO2 Beetle Counter and Pollen Glass Series 40 mm)

The SUIKEI detailed data