Ecology of the Planted Aquarium should appeal to hobbyists who wish to set up a successful planted aquarium plus understand more about its ecology.
Most aquarium plant books simply list/describe plant species or show how to set up a planted aquarium. This book is unique. For it explains the underlying mechanisms of the aquarium ecosystem– how plants affect the ecosystem and how the ecosystem affects the plants. It shows that plants are not just decorative but can also be quite useful in keeping fish healthy and reducing aquarium maintenance.
In addition, my book presents extensive scientific information that hobbyists have never seen. This information often contradicts prevailing ideas in the aquarium hobby– ideas that are often based on antiquated books and hobbyist observations rather than experimental data.
Aquatic plants studied include those from ponds, lakes, wetlands, and oceans. Many of the plants, such as Vallisneria, Hornwort, and Cabomba, are familiar to aquarium hobbyists. Others such as pondweeds and marine seagrasses may not be. However, aquatic plants, whether from the ocean or a tropical stream, have many of the same basic needs and physiology. Thus, concepts drawn from scientific studies of ‘aquatic plants’ can often be applied to ‘aquarium plants’. In my opinion, any distinction between the two is obscured by the great diversity of species used by both aquarium hobbyists and aquatic botanists.
Although the book is directed toward aquarium keeping, many of the concepts apply equally to ornamental pond keeping. On occasion, I have noted where there might be differences.
In order to make the scientific studies more relevant to hobbyists, I have interspersed the text with typical or actual ‘Questions and Answers’ (Q & A). These Q & A, plus practical discussions at the end of chapters, show how the scientific information applies to hobbyists’ aquariums. The last chapter describes how to keep aquariums that are inexpensive and simple to maintain.
The chapters of this book are grouped around the three goals of the book, which are to discuss: (1) how plants affect the aquarium ecosystem; (2) what factors affect plants; and (3) how hobbyists can use this information to maintain a successful home aquarium.
The introduction briefly describes the purpose and organization of the book and the characteristics of a ‘healthy’ aquarium.
In Chapter II the toxicity of water contaminants– heavy metals, ammonia, and nitrite– to fish and plants are discussed. I show how plants counteract those toxins to purify the water and protect fish.
Allelopathy, defined as chemical interactions between organisms, is most likely rampant in home aquariums. I present scientific evidence for allelopathic interactions between aquatic plants, algae, bacteria, invertebrates, and fish. I list specific chemicals isolated from a variety of aquatic plants and then list the organisms these chemicals have been shown to inhibit. Finally, I speculate on how allelopathy affects aquarium keeping.
In Chapter IV, I classify different bacterial processes in terms of their positive and negative impacts on the aquarium. Topics include the generation of plant nutrients, CO2, and humic substances by heterotrophic bacteria. In addition, I explain how bacterial processes both create and destroy aquarium toxins.
Chapter V compares three potential sources of plant nutrients in aquariums– fishfood, a soil substrate, and tapwater. I use a model aquarium to quantify the theoretical contribution from each source. I show that fishfood contains all elements that plants require and that soil abundantly supplies most micronutrients. I compare hardwater versus softwater as a nutrient source. In the final analysis, I discuss which of the three sources best provides each nutrient.
Carbon is briefly described in terms of alkalinity and water buffering, and then more thoroughly as a plant nutrient. I show that the element carbon often limits the growth of submerged plants both in nature and in aquariums. I describe strategies that aquatic plants use to obtain carbon. Finally, I show how hobbyists can help provide their aquarium plants with more CO2.
Chapter VII describes the fundamentals of aquatic plant nutrition. Thus, the required elements and their chemical (nutrient) form are listed, along with each element’s function. Substrate versus water uptake of nutrients is discussed. I show that aquatic plants prefer ammonium over nitrates as their nitrogen source and why this makes biological filtration less critical in aquariums with plants. I discuss how the water chemistry of a plant’s natural habitat influences its nutrient requirements.
Most hobbyists do not have soil substrates in their aquariums, which may be the main reason they have trouble growing plants. For a better understanding of this critical topic, Chapter VIII discusses the general nature of soils before delving into the even greater complexities of submerged soils. Finally, it describes how hobbyists can use soils in the aquarium effectively.
In Chapter IX, I discuss the major problems that submerged aquatic plants face and why emergent plants do so much better. For the hobbyist, I describe how to promote aerial growth to optimize the aquarium ecosystem.
Chapter X focuses on a major problem that many aquarium hobbyists have– tanks overrun by algae. Common methods that hobbyists use to counteract algal problems are evaluated. I then discuss additional factors that the hobbyist can use to control algae. I show how hobbyists can successfully rid their tanks of algae without destroying the ecosystem.
In my opinion, planted aquariums are much easier to maintain than those without plants. Plants control alga growth and keep the tank healthy for fish without the drudgery of frequent water changes and gravel cleaning. In Chapter XI, I describe how I set up my planted tanks, which are both inexpensive and easily maintained. I also present my own guidelines as to fish, lighting, substrates, filtration, etc that the hobbyist can use to set up similar tanks.
Older aquarium books advocated the “Balanced Aquarium” in which plants and fish balance each others needs. Intrinsic to the idea of the balanced aquarium was the healthy growth of plants, but many hobbyists found planted aquariums difficult to maintain. Poor plant growth and unrestricted algal growth were persistent problems. Thus over the years, the idea of having a natural, planted aquarium lost its original appeal [1]. Many hobbyists gave up on the idea and dispensed with live plants altogether.
Furthermore, many aquarium hobbyists and retailers have little interest in plants, being primarily interested in keeping and breeding fish. Often the methods they use and recommend are not conducive to growing plants. For example, optimal fishkeeping without plants often depends on enhanced biological filtration, strong aeration, undergravel filters, and frequent tank cleaning. Beginning hobbyists that try to adapt these methods to growing plants in their aquariums often fail.
Other hobbyists, mainly from Europe and within the last 20 years, developed techniques for growing plants in the aquarium that were highly successful. The sophisticated technology they used consistently produced beautiful, planted aquariums, which I will call ‘High-tech’ aquariums. The end result did, indeed, resemble ‘a slice of nature’. Unfortunately, the artificial methods to obtain such an aquarium ignored many of the natural processes of bacteria and plants. The end result– healthy fish and plants– resembled the natural, balanced aquarium, but the means to obtain it were unnatural, expensive, and laborious.1
With this book, I would like to resurrect the older version of the natural, planted aquarium but with a much greater understanding of how it works.
The ‘Low-tech’ aquariums that I maintain are characterized by a small or moderate number of fish, reduced filtration and cleaning, a large number of healthy growing plants, and diverse microorganisms. Essential to my natural aquarium is moderate lighting, a substrate enriched with ordinary soil, and well-adapted plants. It differs from what many hobbyists are familiar with– dimly lit tanks with gravel substrates.
Q. I use a pH adjuster (containing dibasic phosphate) to keep the pH up, because the water constantly tends to acidify. The plants aren’t growing as well as I would like. Do you think the phosphates in the pH adjuster will encourage algae?
A. They might, but the bigger problem is that your tank is going acid over time. In many aquariums, nitrification in the filters is the source of the acidity. In ‘fish only’ tanks it can’t be helped, but in planted tanks photosynthesis, denitrification, and other powerful acid-neutralizing processes keep the pH up.
The only tanks I have had “go acid” are those with poor plant growth, or those without soil in the substrate. Normally, my planted tanks show a neutral or alkaline pH. Base-generating reactions counteract acid-generating reactions. I would work on encouraging total plant growth in your tank.
At the same time, it differs from the Hightech tank in that it takes greater advantage of natural processes. The Low-tech aquarium is easier (and much less expensive) to set up and maintain. This is because natural processes are taken full advantage of. For example, bacteria and fish– not artificial CO2 injection– provide CO2 to plants. Plants and soil bacteria– not trickle filters– remove ammonia from the water and protect fish. Fishfood and soil– not micronutrient fertilizers– provide trace elements to plants.
What are some specific characteristics of Low-tech aquariums?
One criterion to gauge an aquarium’s success is a stable pH; acid-generating reactions in the tank are matched by base-generating reactions. Tanks with water that become acidic over time are unbalanced, usually due to excessive nitrification in the filter. Table I-1 lists the biological and physical processes that affect the pH in aquariums.
Table I-1. Major Processes that Affect Aquarium pH.
| Acid-Generating Processes (pH goes down) | Base-Generating processes (pH goes up) |
| Respiration of fish | Photosynthesis by plants and algae |
| Nitrification by filter bacteria | Denitrification by bacteria |
| Bacterial metabolism (e.g. decomposition of organic matter) | Water and air mixing (loss of CO2) |
The hallmark of a Low-tech aquarium is that it is easily maintained. Aquariums seem to do well without hobbyist adjustment, maintenance, and cleaning. For example, my own aquariums often go for six months or more without water changes. Fish get fed well, so that plants do not need to be fertilized artificially. The only routine maintenance is replacing evaporated water and pruning excess plant growth. Tanks that are unbalanced need constant cleaning and adjustment.
Normal fish behavior is a good indicator of a healthy, balanced ecosystem. In tanks, this means that vigorous fish like Rainbows and cichlids should be thrashing over food at meals. Male guppies should be actively courting female guppies.
Abnormal fish behavior (not eating) or an inability to reproduce often indicates contaminated water. For example, otherwise vigorous fish will stop eating when water nitrite levels get too high.
Below are the benefits that plants– given a chance– play in the aquarium:
1. Protect fish by removing ammonia. Plants readily take up ammonia, which is toxic, even though there may be adequate nitrogen in the substrate or plentiful nitrates in the water. This is because aquatic plants have a decided and overriding preference for ammonia (see pages 107-108).
2. Protect fish by removing metals from the water. Heavy metals may or may not directly kill fish, but they can inhibit reproduction and suppress normal appetite, such that the fish eventually succumb to disease. Plants rapidly take up large quantities of ‘heavy metals’ like lead, cadmium, copper, and zinc from the water. Also, plant decomposition produces humic substances, which bind and detoxify metals (see pages 14-16).
3. Control algae. Good plant growth seems to inhibit algae, whether in nature or aquariums. How plants do this is not certain. However, plants produce and release a wide variety of allelochemicals that are mildly toxic to algae (see pages 41-43). Plants also readily remove iron from water, thereby depriving algae of an important nutrient (see pages 167-170).
4. Stabilize the pH. Photosynthesis is a major acid-consuming reaction. Thus, vigorous plant growth keeps the water from becoming acidic over time.
5. Increase biological activity within the tank. Most microorganisms (bacteria, protozoa, fungi, algae, etc) do not live freely in the water but live attached to surfaces. Plants, especially the roots of floating plants, provide an ideal home for numerous microorganisms (see page 153), many of which recycle nutrients and stabilize the aquarium ecosystem.
6. Oxygenate the water. Actually, the air probably provides more oxygen consistently to fish than plant photosynthesis. And while it is true that plants also consume oxygen (plants ‘breathe’ just as humans do), healthy plants give off far more oxygen via photosynthesis than they consume by respiration. Even when plants are not photosynthesizing, such as at night, they probably remove less oxygen than one would expect. This is because they prefer to use the oxygen stored in their tissues rather than take up oxygen from the water.2
7. Remove CO2 from the water. Excess CO2– as much as oxygen depletion– can cause respiratory distress in fish (fish gasping at the surface [6]). Normally, plants would be expected to remove all CO2 from the water during daylight hours.
8. Prevent substrates from becoming toxic. In my experience, a substrate that supports good plant growth doesn’t become toxic, and it rarely (if ever) needs to be vacuumed. Plant roots keep it healthy (see page 135-136).
Q. My Black Moor has been sick for the last two weeks. It seems to be losing its scales and has white stringy stuff on its body. Its body is now gray-colored, instead of its original dark brown color. I keep the Moor in a small 2 gal tank with no plants, but it has a small box filter and I do 10-20% water changes every week.
I have another tank, a 10 gal with heavy plant growth with many red swordtails (including babies) that are doing fine. Should I try antibiotics?
A. Poor aquarium conditions may have lowered your fish’s immunity to natural bacteria. Antibiotics might cure the immediate infection, but they won’t help much to counteract the underlying problem-- a toxic substrate, contaminated water, etc. I would either clean the tank or transfer the Black Moor to the planted tank.
Results: I put the Moor into the planted tank. Within 2 weeks his problems cleared up. He is now eating all the snails in the tank!
Analysis: I am delighted to hear that your Black Moor has regained his health. Plants in the aquarium are much more than decoration or hiding places for fry. They protect fish by improving water quality (e.g., counteracting heavy metal and ammonia toxicity, removing excess CO2, oxygenating the water, etc).
Many hobbyists would like to keep plants in their aquariums, but repeated failures or the expense of the High-tech systems has discouraged them. Thus, the rest of the book addresses the factors that affect plant growth in the aquarium. They are:
1. Nutrients. Tapwater, a soil substrate, and fishfood can easily provide all nutrients required by aquarium plants (see Ch V ‘Sources of Plant Nutrients’).
2. Algae Control. Plants cannot grow if algae smother them. Practical strategies, both short-term and long-term, for controlling algae are discussed in Ch X ‘Algae Control’.
3. Fertile substrates. Theoretically, aquatic plants can get all nutrients from the water, so what’s wrong with a gravel substrate? However, in practice, gravel substrates do not work very well. Plants need a fertile substrate to grow well and compete with algae. (See Ch VIII ‘Substrates’.)
4. Bacteria. Bacteria break down organic matter into CO2 and other nutrients that plants can use. The complex and interesting role bacteria play in aquarium ecology are described not just in Ch IV (‘Bacteria’) but throughout the book.
5. Aerial (Emergent) Growth. Plants that access air for light and CO2 grow much better than fully submerged plants (Ch IX ‘The Aerial Advantage’). By using floating plants and encouraging other forms of aerial growth, hobbyists can increase total plant growth in the aquarium.
6. Light. Adequate light is essential for growing plants effectively in the aquarium. In Ch XI (‘Practical Aquarium Setup and Maintenance’), I discuss using light in the home aquarium for optimal plant growth.
7. Plant Species. Different plant species may respond differently to individual tank conditions, such as lighting, substrate, water chemistry, CO2, and other plant species in the tank. New tanks set up with a wide variety of species have a better chance to do well.
REFERENCES
1.Atz JW. 1952. The balanced aquarium myth. In: Axelrod HR (Ed.). Tropical Fish as a Hobby. McGraw-Hill (New York), pp 215-227.
2.Horst K and Kipper HE. 1986. The Optimum Aquarium. AD aquadocumenta Verlag GmbH (Bielefeld, Germany).
3.Dennerle L and Lilge H. System for a Problem-Free Aquarium. Dennerle GmbH (Germany).
4.Booth G and Booth K. 1993. Some assembly required (Pt 8). The Aquatic Gardener 6(4): 109-116.
5.Wetzel RG. 1983. Limnology (Second Ed.). Saunders College Publishing (Philadelphia, PA), p. 529.
6.Reid SG et al. 2000. Cardiovascular and respiratory reflexes in the tropical fish traira (Hoplias malabaricus): CO2/pH chemoresponses. Respiration Physiology 120: 47-59.
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1High-tech aquariums are sponsored by the two European manufacturers Dupla and Dennerle. The complete systems, which require metal halide lighting, CO2 injection with automatic pH regulation, trickle filters, daily plant fertilization, and substrate heating cables [2,3], are quite expensive. For example, two hobbyists [4] report that the set-up for their 90 gal ‘Super Show Tank’ based on the Dupla system cost more than $3,500.
2During photosynthesis, oxygen accumulates rapidly within the plant lacunae, which are huge gas storage chambers making up about 70% of the plant’s interior. This internal oxygen is used for the plant’s respiration both day and night [5].