Balancing Light and CO2 in the Nature Aquarium

Author: Takashi Amano

This month the aquatic plant layout expert discusses proper lighting and CO2 injection in the Nature Aquarium and how to keep these elements in balance.

Proper lighting and CO₂ injection are essential for growing healthy aquatic plants and creating a beautiful aquatic plant layout. It is important to keep these elements in balance in order to grow multiple types of aquatic plants abundantly, and grow every one of them well, as is accomplished in the Nature Aquarium. Light and CO₂ are to aquatic plants as wheels are to a bicycle—if one is missing, things do not work properly. Although some people keep the lighting intentionally dim to avoid the emergence of algae, this is not a desirable condition for aquatic plants. Aquatic plants grow healthy when an adequate amount of light is provided and the proportionate amount of CO₂ is injected. In turn, the emergence of algae is suppressed as well.

Photosynthesis Basics

Aquatic plants grow healthy only when they can photosynthesize sufficiently. Although some aquatic plants appear to photosynthesize vigorously while others do not, they all photosynthesize to varying degrees.

Stem plants, Riccia, Glossostigma, hair grass, and the various Echinodorus species are the light-loving plants that photosynthesize vigorously under a strong light, releasing a lot of oxygen bubbles in the process. In contrast, Cryptocoryne and Anubias species are shade-loving plants that grow well under relatively weak lighting and don’t photosynthesize vigorously. Ferns such as Bolbitis and mosses like willow moss also tolerate shade well, growing well under relatively weak light.

These shade-loving plants do photosynthesize, but they do it slowly and more gradually dissolve oxygen into the water. It is important to understand the different light requirements of various aquatic plants in order to create a beautiful Nature Aquarium.

Adjusting Aquarium Light Intensity

Suppose we use both light-loving plants and shade-loving plants as the main components of a layout. In mix of plants with varying lighting needs, the intensity of the light should be matched to the level where the light-loving plants grow well.

For example, for a W90- x D45- x H45-cm (36- x 18- x 18-inch) tank of approximately 180 liters (about 50 gallons), a single 150W metal halide lamp or a 150W metal halide lamp with two 36W power compact (PC) lamps would be used to create a typical Nature Aquarium setup. Just about all light-loving aquatic plants grow well under this intensity, but it’s not too strong for most shade-loving plants.

For a smaller size tank, for example a W60- x D30- x H36-cm (24- x 12- x 14-inch) tank of approximately 60 liters (about 15 gallons), two 36W PC lamps are used. On the other side of the equation, for a large W180- x D60- x D60-cm (72- x 24- x 24-inch) tank of approximately 680 liters (about 180 gallons), I would use three 150W metal halide lamps.

I have created many Nature Aquarium layouts, and I have found through my experiences that these are the lighting conditions that enable aquatic plants to grow healthy. Red stem plants do not grow well unless an adequate amount of light is provided, so I decide on the brightness levels using them as criteria. If normally red submersed leaves do not turn red, it could be due to insufficient lighting. If the light is not sufficient, the nodes of stem plants elongate and Glossostigma grows upward. If you see such symptoms of insufficient lighting, provide a brighter lamp or increase the number of lamps. As an alternative to adding lighting to the tank, if light-loving plants fail to grow well due to insufficient lighting, you can also change the layout to the one that is planted mainly with shade-loving plants.

Adjusting CO₂ Injection

Once the lighting intensity is settled, CO₂ injection volume is adjusted next. Although CO₂ injection is pretty common nowadays, it wasn’t always considered a necessity. The CO₂ that dissolves into the water from the water surface was thought to be sufficient. However, when a large amount of aquatic plants photosynthesize all at once in the limited space of an aquarium, the small amount of CO₂dissolved from the water surface is used up quickly. This becomes more evident as the volume of aquatic plants or the light intensity increases.

In the Nature Aquarium, CO₂ is injected into the aquarium to encourage photosynthesis of aquatic plants using a cylinder of liquid carbon dioxide gas, a CO₂ regulator, and a CO₂ diffuser. The simplest and the most objective way to figure out the CO₂ concentration in water is to measure its pH. CO₂ dissolved in water has the ability to reduce pH, turning the water acidic. On the other hand, pH rises as the amount of CO₂ in the water decreases from the photosynthesis of aquatic plants, turning the water alkaline. Therefore, you can judge the CO₂ concentration by measuring the pH of the water.

We define the standard value as the pH value just before the light is turned on in the morning (before CO₂ injection begins for the day), after sufficient aeration throughout the night. If the pH value measurement is higher than the standard value four to five hours after the start of the CO₂₂ injection is insufficient. If the measured value is slightly lower than the standard value, the amount is adequate. If the measured value is much lower than the standard, the amount is excessive. injection, the amount of CO.

Although I sometimes use a pH probe in a large aquarium to measure the pH constantly, for a small aquarium or if a pH meter is not available, I recommend measuring pH two to three times a day with a pH indicator solution and use the measurements as a guide for the CO₂ injection volume. You should observe your fish and shrimp very carefully on the first day that you start injecting CO₂; fish and shrimp suffer from lack of oxygen if a CO₂ injection volume becomes excessive.

With adequate lighting and CO₂ injection, aquatic plants will photosynthesize vigorously, allowing the abundant plant life in the Nature Aquarium to flourish.

Lighting and CO2 Examples

DATA

Aquarium: Cube Garden Mist, W60 x D30 x H36 (cm)

Lighting: Solar II (NA 36W PC x 2), turned on for 10 hours per day

Filter: Super Jet Filter ES-600 (Bio Rio)

Substrate: Aqua Soil, Power Sand Special S, Bacter 100, Clear Super, Tourmaline BC, Penac W/for Aquarium, Penac P

CO₂: Pollen Glass, 3 bubbles per second via CO₂ Glass Counter (using Tower/20)

Aeration: 14 hours after the light is turned off using Lily Pipe P-2

Additives: Brighty K; Green Brighty STEP2; Green Brighty Special Lights

Water change: 1/3 once a week

Water quality: Temperature 26ºC, pH 6.8, TH 20 mg/l

Aquatic plants: Glossostigma elatinoides, Echinodorus tenellus, Anubias barteri var. nana “narrow,”Microsorium pteropus “narrow,” Myriophyllum mattogrossense “green,” Rotala sp., Rotala sp. “Nanjenshan,” Micranthemum umbrosum, Ludwigia arcuata, Rotala sp. “ceylon,” Eusteralis sp., Rotala sp. “green,” Riccia fluitans, Fontinalis antipyretica

Aquatic animals: Inpaichthys kerri, Hyphessobrycon herbertaxelrodi, Hyphessobrycon sp.,Hyphessobrycon amandae, Otocinclus sp., Caridina japonica

[Note: The hardware itemized above represents the author’s specific choices; equivalent results may be obtained with other equipment and accessories—Eds.]

DATA

Aquarium: Cube Garden Clear, W90 x D45 x H45 (cm)

Lighting: Grand Solar I (NAHM-150W x 1, NA 36W PC x 2), turned on for 10 hours per day

Filter: Super Jet Filter ES-600

Substrate: Aqua Soil, Bright Sand, Power Sand M, Bacter 100, Clear Super, Tourmaline BC, Penac W/ for Aquarium, Penac P

CO₂: Pollen Glass Beetle 40, 2 bubbles per second via CO₂ Glass Counter (using Tower/20)

Aeration: 14 hours after the light is turned off using Lily Pipe P-2

Additives: Brighty K; Green Brighty STEP2

Water change: 1/3 once a week

Water quality: Temperature 25ºC, pH 6.8, TH 50 mg/l

Aquatic plants: Fontinalis antipyretica, Eleocharis acicularis

Aquatic animals: Paracheirodon innesi, Crossocheilus siamensis, Caridina japonica