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Plants and animal life in a balanced aquarium

Plants and animal life in a balanced aquarium

Introduction: (Initial Observation)

Every time that I buy a pair of gold fishes, they die in a few weeks. I change the water regularly, use chemicals to remove chlorine, add fish food, but nothing works and they die anyway. I remember my grand mother’s house had a pool full of gold fishes that had lived there for many years.

Her pool was full of dirty greenish water, algae and many worm like creatures.

How come my gold fishes die in clean water with good food and hers stay alive with no food and no care what so ever?

In this project I will research plants and animal life in a balanced aquarium in order to find out how do these organisms affect each other. I may discover that fish, algae, plants and those worm like creatures actually help each other to survive or provide food for each other.

What you see above is just an example of initial observation that leads to choosing a subject for research.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.  

Project advisor

Problem statement:

The idea of a science project usually starts by a question or a problem. This is a sample problem for a balanced aquarium project.

Every time I bought a few fishes and set up a simple aquarium, they died after a few days. I provided them with clean water, sufficient food, enough light and comfortable room temperature, but they died any way. I was wondering “How can fishes live in dirty ponds and die in my clean jar?”. Maybe the algae and plants that I think of them as dirt, are really beneficial for fishes. I have selected this project idea hopping that I will learn something from it so my fishes will not die any more.

Information Gathering:

In order to find information about a balanced aquarium, search the internet or a library with the exact keyword of “balanced aquarium“. your search will give you some valuable information and possibly two other related keywords that are “echo system” and “homeostasis“. Search about these two new keywords and you will find more details.
When living things interact, each organism contributes its own special properties to another. These organisms work together to benefit the environment in which they are a part of. You can experiment to see see how homeostasis can be achieved in an aquarium.

Following are some links related to balanced aquarium.


The Four Truths of Aquarium Keeping







Following are a clear description of how a balanced aquarium works?

Following are a clear description of how a balanced aquarium works?

Introducing fish, plants and food to your aquarium begins a natural process called the nitrogen cycle. Food which is consumed by your fish provides them with energy. This energy in turn is burned with the help of oxygen which your fish breathe from the water.


During the energy burning process, waste is returned to the aquarium environment via the fish’s gills. The waste primarily consists of carbon dioxide and nitrogenous compounds such as ammonia. In order to maintain a healthy environment, these wastes must be removed. The carbon dioxide is mainly eliminated through either aeration at the surface of the tank or through photosynthesis by aquarium plants. As for the toxic nitrogenous compounds, they are converted to less toxic compounds via the nitrogen cycle. Natural bacterial colonies convert toxic nitrogenous compounds and ammonia into harmless products.

The entire process begins with the conversion of solid wastes excreted by fish into ammonia. Bacteria known as nitrifiers include two “microbial partners” which transform potential toxic nitrogen compounds into nitrite and nitrate via biochemical oxidation.

Both bacteria prefer alkaline environments (pH 7.2 – 8.5). However a stable and consistent pH level is important.

Nitrifiers are most active at temperatures ranging from 68 – 86 degrees F. Their metabolism will decrease below 50 degrees F, while levels above 95 degrees F are potentially life threatening.

Following are two definitions for homeostasis:


Any self-regulating process by which a biological or mechanical system maintains stability while adjusting to changing conditions. Systems in dynamic equilibrium reach a balance in which internal change continuously compensates for external change in a feedback control process to keep conditions relatively uniform. An example is temperature regulation–mechanically in a room by a thermostat or biologically in the body by a complex system controlled by the hypothalamus, which adjusts breathing and metabolic rates, blood-vessel dilation, and blood-sugar level in response to changes caused by factors incl. ambient temperature, hormones, and disease.


A built-in, automated property of a system that executes and monitors events essential to the existence of the system, such as animal breathing and instinct. It is a self-regulating mechanism that allows a system to avoid paying detailed attention to its most basic functions thereby helping keep it in a steady state.

Question/ Purpose:

The purpose of this project is to study plant and animal life in a balanced aquarium. We will try to find out how do the plants and animals in an aquarium affect each other.

Identify Variables:

Independent variables are: organisms such as plants and animals in an aquarium.

Dependent variables are: life (Length or quality) of animals and plants in an aquarium.

By classifying our variables in two types of dependent and independent, we are making it clear that organisms such as plants and animals that we choose to live in an aquarium, may affect the length or quality of the life of such plants and animals.


My hypothesis is that plants and animals in an aquarium will be beneficial for each other. In other words I think both animals and plants will have a healthier an d longer life when they live with each other than when they are alone. This hypothesis is based on my observations of lakes, swamps and ponds that are home or habitat for a combination of animals and plants.

Experiment Design:

Experiment 1:

To test how plants and animals affect each other’s life, we set up three aquariums.

Any clear glass or plastic container with a wide opening on top can be used as an aquarium in this experiment.

Contents of aquariums will be as follows:

  • First aquarium will only have fishes. A pair of inexpensive gold fish is sufficient for this test.
  • Second aquarium will only have plants. Your local pet store or aquarium shop can help you to select the plant. The least expensive, but healthier plant is what you need for this experiment.
  • Third aquarium will have both fishes and plants.

All three aquarium must be the same size. They should also have the same amount and the same type of aged water. The number and size of fishes in aquarium one and three must be the same. Also the amount and type of plants in aquarium 2 and 3 must be the same.

If you add any fertilizer for plants or any food for fishes, add them in all three aquariums even the one that has no plants or fish. We do this to keep all three aquariums in the same condition. For the purpose of this experiment you may decide not to use any food or fertilizer at all. To make aged water, keep tap water in a wide open container for about 24 hours.

The big problem in overfeeding is that fish will eat whether they need it or not. Whatever is left comes out the other end. Or even worse, left over food falls to the bottom of the tank to rot and pollute the water.

The way I feed is to use a small enough portion of food so that it is gone in 30 seconds. If the fish still act hungry, I will feed them again LATER. If you need to feed more than this in order to get certain fish to be able to eat, you have a compatibility problem, not a food problem.

Place the aquariums somewhere with enough indirect light.

Inspect your plants and fishes every day at the same time and record your observation in a table like this:

Results Table: Condition of plants and animals in 3 test aquariums.

Aquarium 1 fishes Aquarium 2 plants Aquarium 3 fishes Aquarium 3 plants
Day 1
Day 2
Day 3
Day 4
Day 5
Day 6
Day 7

Continue your observations until you see an obvious change in your plants or animals.

What may happen?

Plants and fishes may die or get sick because of toxic material, harmful bacteria or parasites. What you can write in your table to describe the condition of your plants or animals are words or numbers. Words can be excellent, good, normal, sick, dead or anything in between. Numbers can start from 100 as the best possible condition to 0 as the worst condition or dead.

Experiment 2:

Get a large glass jar with lid or small aquarium, add some clean gravel, aged tap water, 4-5 guppies, 2-3 snails and 1-2 water plants. You should find the effect of each plant or animal in a balanced aquarium.

Materials and Equipment:

List of material can be extracted from the experiment section.

Results of Experiment (Observation):

The completed table from the experiment section is the result of your experiment.


If you do any calculation related to this project, write them here for your report.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

1. What do snails use for food?
2. Why are plants important to this environment?
3. What do fish provide to the environment?
4. Describe the interaction of the plants, guppies and snails

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.


List of References