Jonah's Aquarium

Email -

Aquarium Basics
For the first time fish keeper
©2000 Jonah's Aquarium

Here are the bottom line essentials for a successful aquarium:


Tank Size

In general, the larger the tank, the better your chances of success. There are many reasons for this. First, the most dangerous threat to fish survival is the waste that the fish themselves produce. This consists of solid waste and ammonia along with other organic chemicals. The really bad part is the ammonia. If you put a fish in a small container and feed it, it will quickly produce enough ammonia to poison itself. If you put the same fish in a large container, the ammonia it produces will be diluted in the larger volume of water. If the ammonia is sufficiently diluted, it is essentially non-toxic to the fish. This is not a permanent solution, but a large tank will give you more room for error than a small tank.

Another reason that a large tank is more likely to be successful is related to fish behavior. Many kinds of fish are accustomed to having a certain territory or space that they occupy and other fishes do not. Kind of like personal space. Under certain conditions, a fish that feels crowded may even kill other fish that it feels are too close. In addition to the territory issue, most fishes will eat other fishes given the chance. So a large aquarium will help reduce the chances that your fishes will kill or eat one another.

There's another phenomenon that comes into play with tank size selection. It's called bare tank syndrome. Few fish keepers are immune to it. Here's how it happens - "Wow, my new fish are really cool! But I hardly have any fish in this tank at all! Hey, those other fish are really cool too! I want some of those! I want my tank to be full of fish, right now!" So the tendency is for the fish keeper to quickly fill the tank with lots of fishes. Reference the above paragraphs on ammonia and territory. A larger tank will safely hold a lot more fish than a smaller tank.

So what's the final analysis? Get as large a tank as you can afford and have room for.


Water Quality

Humans live in an environment of air. We take in everything that is in the air around us. Fish live in water. Whatever is in the water will get into the fish. Not only that, but the water is the same water in which the fish go to the bathroom. How would you like to spend your entire life in the bathroom?! That bring us back to the problem of ammonia. How can you remove the ammonia that the fish are producing all of the time? One quick solution is to remove some of the contaminated water and replace it with clean water. This works...if you do it every day. But there's an easier way. Turns out that, though ammonia is toxic to fish, it is tasty to certain microorganisms: bacteria. Certain types of bacteria will actually eat the ammonia. So all that's needed is to get enough of these bacteria living in the tank to remove all of the ammonia. And the really nice thing about these bacteria is that they need the same environment to live that the fish need to live. They need water, oxygen and ammonia. So if we can keep the bacteria alive, we can take advantage of biological filtration to remove the ammonia that is harmful to the fishes.

Biological filtration is absolutely essential to a successful aquarium. So how is this done? The bacteria that eat the ammonia need to have a surface to live on and water flowing over them to provide a supply of dissolved oxygen. We won't get into a long discussion of oxygen right now, but water that is flowing and can come into contact with air, will absorb enough oxygen to sustain bacteria and fish. All we need to do is set up a system that will supply a home for the bacteria with water flowing through it. This begins our discussion of filter systems. Most commercially available filters are designed to perform several functions at once. The only one of these functions that is critical to your fish is biological filtration. Following is a simplified description of some basic filter types -

Undergravel Filter

The Undergravel Filter is one of the simplest types of aquarium filters. It consists of a slotted plastic plate that rests on the bottom of the aquarium and covers the entire bottom of the tank. There is a space underneath the plate that allows water to flow through. Suitable aquarium gravel is layered on top of the plate to a depth of two to four inches. There are one or more lift tubes that come out of the plate and extend up through the water to near the surface. An air pump or water pump such as a powerhead is used to pull water up through the lift tubes. The effect is to circulate water down through the gravel, under the filter plate and up and out the top of the lift tubes. The surface of the gravel and other surfaces of the filter plate are where the ammonia-eating bacteria will live. As long as the water continues to flow through the gravel and out through the lift tubes, the bacteria can survive and multiply. The more bacteria that can grow, the more ammonia they will consume. It's like a built in sewage treatment plant. But if the water stops flowing, the bacteria will die and the ammonia will accumulate.

Power Filter or Outside Power Filter

The Power Filter or Outside Power Filter is a very common type of filter for aquaria. It consists of a plastic box that hangs on one side of the tank on the outside. Water is pumped up through a lift tube, out of the tank and into the box. The water flows through various filter media and then is returned to the tank, usually by an outflow chute. The principle is essentially the same as the undergravel filter, except that the gravel is replaced by some other, artificial media that bacteria can grow on. This may be a plastic screen, a sponge, ceramic cylinders, or any number of other materials. Each brand has its own type of media. Again, the bacteria will live and consume ammonia as long as there is oxygenated water flowing over them.

Canister Filter

The canister filter is similar to the outside power filter except that it's usually placed on the floor or inside of a cabinet stand, rather than hanging on the side of the aquarium. It consists of a sealed container or canister with two plastic tubes that carry water from the aquarium to the canister and from the canister to the aquarium. Inside of the canister are the various types of filter media as in the power filter. And as in the power filter, the ammonia-eating bacteria will live and consume ammonia as long as there is oxygenated water flowing over them.

Sponge Filter

Sponge filters are made in various shapes and sizes for various applications. They consist of a large piece of foam material with a central core and lift tube that allows water to flow up and out of the sponge. The entire filter is placed inside of the aquarium just as in the undergravel filter. Frequently they have a weighted base to keep them resting on the aquarium floor. The filter can be driven by an air pump or by a powerhead if the lift tube is large enough. The foam or sponge material is the media where the bacteria can live. Water is drawn through the sponge and into the central core where it is pumped out to the aquarium again.

Other Filters

There is a wide variety of other types of aquarium filters. Every aquarist develops their own preference for certain types or combinations of filters. Any filter will work as long as it can support a large enough colony of ammonia-eating bacteria to consume the waste that your fish are producing. The more fish you have, and the more they eat, the more bacteria you must have to consume the waste. You can use more than one filter and more than one type of filter on your aquarium. Some aquarists like to have more than one filter as back up in case one filter fails.


Water Changes

Even if you have plenty of filtration and happy bacteria, this is not a long term solution to eliminating fish waste. The ammonia-eating bacteria are perfect for eliminating the highly toxic ammonia that can quickly kill your fish. But the nitrogen from this ammonia is still in your aquarium. You may hear reference to "the nitrogen cycle". This refers to the various chemical forms that nitrogen from fish waste takes as it is processed by microorganisms in the tank. This process is certainly very complex. But in simple terms, ammonia from the fish is converted to nitrite, and this nitrite is converted to nitrate. A healthy bacterial colony will change all of the nitrite to nitrate. This is important because nitrite is also very toxic to fish. We will discuss this more in the section on new tank cycling. As long as the bacteria can turn the nitrogen into nitrate, your fish are safe for the time being. But over a long period of time the nitrate will accumulate in the aquarium and cause stress for the fish. Some fish are very tolerant of nitrate and others are not. That's why water changes are necessary. The best way to remove nitrate from the aquarium is to remove the contaminated water and replace it with clean water.

Water changes should be done on a regular schedule. How often depends on how many fish are in the tank, how much they are fed, and the size of the tank. Again, a larger tank allows more room for error with water changes. In most cases, the more often the water is changed, the better. A conservative standard would be once per week. Test kits can be used to actually measure the amount of ammonia, nitrite and nitrate in the aquarium. This may be important for a new tank as the bacteria are getting established. If you don't want to buy a test kit, a good local aquarium store will test the water for you if you bring them a sample in a clean jar. If you're not sure whether a water change is needed, go ahead and do it. Clean water is healthier for your fish than dirty water.

Water Change Procedure - You can change as much or as little of the aquarium water as you like. As a general guide, remove one quarter to one third of the water and replace it with clean water. The water you use to refill the tank must be free of chlorine, oxygenated, and the same temperature as the water in the tank. Certain types of fish may also be sensitive to the pH and hardness of the water. Check with your supplier about this.

Chlorine - Chlorine and chloramine (a compound of chlorine and ammonia) are used to treat public water in most cities. These chemicals are intended to kill harmful bacteria. As a side effect, they will kill all bacteria and other aquatic life, including fishes. Unless you are certain that your water supply comes from an untreated well, you must remove the chlorine and ammonia before adding the water to your aquarium. The easiest way to do this is to use a water conditioner/dechlorinator. A myriad of products are available for this. Any of the commercial dechlorinators should work if used at the recommended dosage. You can add the dechlorinator before you put the water into the aquarium or add it along with the clean water. If you add it as you add the water, never add more than one half of the volume of water that is still in the tank. This will be equal to a one third water change. Here's an easy way to calculate the portion -

Use a ruler to measure the height of the water in the tank above the gravel. Measure from the top of the gravel to the surface of the water along the outside of the tank. Divide this number by three. The result is the amount of water in inches that you will remove to perform a one-third water change. For instance, if the height of the water is 15 inches, 15 divided by 3 is 5. Remove five inches of water from the tank. If you refill this five inches of water with clean water, you can add the dechlorinator while you add the water because the volume you're adding is only one half of the volume that is already in the tank.

If you remove more than one third of the water from the tank, measure the height of the water after you have removed as much as you want to. Take the height of the remaining water and divide it by two. The result is the height you can add to the water that is already in the tank. For instance, if you have 10 inches of water in the tank (above the gravel), you can add 5 more inches, for a total of 15 inches in the tank. Once you add the five inches of water and the dechlorinator, wait 5 to 10 minutes for the dechlorinator to mix in and destroy the chlorine. Then repeat the procedure with another half portion of what is now in the tank - 15 divided by 2 equals 7.5 more inches of water, or to the top of the tank, which ever is less. Don't forget the dechlorinator!

If all that seems too complicated, just mix the dechlorinator with the water before you add it to the tank. You will need a mixing container, such as a five gallon bucket for this. Always make sure the water you are adding to the tank is the same temperature as the water in the tank. Use a thermometer to measure the temperature of both.

Oxygenation - We mentioned earlier that the water you use for your aquarium needs to be oxygenated. This just means that there is a certain minimum amount of oxygen gas dissolved in the water. There's no magic trick to this. Water that is exposed to air will absorb oxygen until it reaches an equilibrium level determined by factors such as atmospheric pressure, temperature and dissolved solids. So all that's needed is that the water you use is exposed to air for a certain period of time before you add it to your aquarium. If you draw water from a tap into a bucket, mix it with dechlorinator, and pour it into your aquarium, that should be sufficient to oxygenate the water. You may find, if your water comes from a well or from a closed container of some type, that it lacks sufficient dissolved oxygen to support aquatic life. In this case, you should leave the water in an open container and perhaps agitate it with an air pump or powerhead for at least 15 minutes. Then it should be safe to add to your aquarium.

Aeration - A more common term that is used by aquarists is aeration. Aeration and oxygenation really mean the same thing. They both mean adding dissolved oxygen to water. When live fish, plants, and bacteria are in an aquarium, they are constantly consuming the dissolved oxygen. (When the lights are on, plants both produce and consume oxygen.) So to insure that the oxygen supply does not run out, the tank water must be aerated. In it's simplest form, aeration is accomplished by circulating the water so that the water at the bottom is moved up to the surface where it comes into contact with the air and absorbs oxygen. If circulation is sufficient, the amount of oxygen that dissolves into the water will exceed the amount that the fish are consuming and everything will work fine. If there is insufficient oxygen, the fish will either come to the surface and gasp for air, or they will become sluggish and ventilate (move their gills and mouths) rapidly. It extreme cases, the fish will begin to die. The same is true for the ammonia-eating bacteria that are needed to remove wastes. You won't see them dying, but ammonia will build up in the tank and hasten the death of your fishes.

Most filter systems will help with aerating the aquarium water by circulating it. Some have a venturi feature that draws air into the out-flow of the filter and brings it into contact with the water. Many powerheads have a venturi feature which is very effective at aerating the water. Filters that are powered by an air pump are constantly aiding aeration by pumping bubbles through the water column. The bubbles themselves are not small enough to dissolve into the water, but the air in the bubbles will dissolve into the water as the bubbles rise. At the same time, the stream of bubbles also pushes water up toward the surface where more oxygen can be absorbed. Air pumps and powerheads can be used apart from filter systems to increase the aeration of your aquarium. Air pumps alone are usually used with some type of airstone or diffuser to create many tiny bubbles.

When deciding what type of aeration you need, several factors should be considered. First of all, warm water will hold less oxygen than cool water. And salty water will hold less oxygen than freshwater. As nitrate and other wastes build up in the tank, the oxygen capacity of the water decreases. So, again, water changes are important for keeping your fish in good health.

Some fishes require a higher dissolved oxygen concentration than do others. In fact some fishes can actually breathe air from the surface of the water and live in very low-oxygen waters. These include gouramis, bettas, bowfin and Corydoras and Hoplosternum catfishes. Other fishes need extra oxygen. Fishes that come from cool, flowing waters or that are highly active swimmers, often need more oxygen than others. Seek advice from knowledgeable sources about the needs of your fishes.

Of course the most obvious factor to consider regarding aeration is the number and size of fish in the tank. The more fish, and the larger they are, the more oxygen that is needed. Avoid crowding the fish, and normal aeration measures will be sufficient.


New Tank Cycling

We have already talked about the nitrogen cycle and the bacteria that change toxic ammonia and nitrite to less toxic nitrate. Now let's talk about one of the most frequent mistakes made by first-time aquarists - New Tank Syndrome. Because the success of our aquarium depends on living bacteria, the aquarist not only has to know how to keep fish alive, he or she also has to know how to keep bacteria alive. And before the fish can live in the aquarium, the bacteria have to be healthy and happy. When a new tank is first set up, everything is essentially dead. You are starting from scratch to create an entirely new ecosystem. Most new aquarists are tempted to quickly acquire lots of fish to populate their new tank. But the fish cannot survive without the unseen bacteria working hard to eliminate the waste. So ammonia and nitrite build up in the tank, the fish become sick or die, and the new aquarium seems like a total disaster. How can this be avoided?

All that's needed is a little self restraint. Get the tank all set up with water, gravel, filter and whatever else you plan to use. Add two fish. Wait for two to three weeks before adding any more fish. If you can make it through those first two or three weeks, you will be home free. That's when the bacteria are growing and colonizing your filter and tank and getting ready to handle all that ammonia from the new fish you will be adding later. And where do the bacteria come from? They come from the two fish you added at the beginning. They picked them up from the aquarium they were in before you got them. If you provide a nice home for them, the bacteria will settle in and grow like crazy. But give them time.

Don't kill your bacteria! You need them. Bacteria will be killed by anything that will kill your fish. That includes lack of oxygen, chlorine, salt, hot water, cold water, and drying out! Certain antibiotic medications used to treat fish will also kill your beneficial bacteria. This is important to know when moving or cleaning your tank and filters. Never use heat or chemicals when cleaning the filter or gravel of an active aquarium. Only use these harsh methods when you want to start from scratch again. Remember, you will have to wait another two or three weeks before you can add more than two fish. For routine cleaning and filter maintenance, Use water taken from your living aquarium ecosystem. This water is free of chlorine and is the right temperature for the living bacteria that are in your filter. To clean a power filter, canister or sponge filter, fill a bucket with water taken from the aquarium. Disassemble the filter and rinse the reusable, non-electrical parts in the bucket of tank water. Immediately reassemble the filter and replace it with the aquarium. Start it running so that the bacteria will continue to get a fresh supply of oxygenated water. Failure to do so will kill the bacteria and require you to start from scratch again with two fish. You will have to find a new home for the others!

Using two or more filters on a tank allows for some backup if one gets killed. If you don't clean them all at once, you will always have at least one healthy bacterial colony to keep your fish safe.

Undergravel filters should be cleaned with a gravel cleaner or gravel vac. There are various types available. They usually consist of a hose with a larger diameter cylinder on one end. The simplest type uses gravity to siphon water from the tank and through the hose into a bucket. As the water is flowing through the hose, the cylinder is used to work the gravel and suck out the solid waste that has accumulated there. This is sometimes called hydro-cleaning. Other types, such as the Python, have a long hose that attaches to a faucet. You turn on the faucet and the water moving through the Python valve creates a suction, drawing water from the tank into the sink or onto the ground if you use an outside spigot. The gravel is worked with the cylinder attachment as in the siphon type cleaner. This uses a lot of tap water, since the water is running the entire time you are cleaning the gravel. The Python can also be used to perform water changes.

If you have an undergravel filter, you can clean the gravel and change the water at the same time. Work the entire gravel area with the gravel vac. It's important to remove the solid waste so that the filter doesn't become clogged. Remember your bacteria are living in the gravel. They need a continuous supply of aerated water to live. Turning off the pumps for a short time during cleaning will not kill the bacteria. Keep this down time to a minimum, though. Replace the water you have removed with clean water as described in the Water Changes section above.

Most filter systems are equipped with mechanical and chemical filter media in addition to the biological media. These may consist of a sponge or filter fiber and charcoal or other types of media and cartridges. Follow the manufacturers' instructions for cleaning and replacing these media. Chemical media, such as charcoal, should be replaced whenever a water change is made on the aquarium. Otherwise, the contaminants that the charcoal has absorbed may be released again into the clean water you have added. In most cases, the chemical media can be permanently removed from the filter. Often, performing regular water changes will accomplish the same result as using chemical media. However, there may be instances when your tap water contains substances you wish to remove. In this case, chemical media, such as activated charcoal, may be useful in adjusting the water chemistry.

Thanks for reading this brief introduction to freshwater aquarium maintenance. There are many books and online resources that can provide additional in-depth information about fish keeping. We sincerely hope that you will have a very successful and rewarding experience with your aquarium.


Jonah's Aquarium Menu

Home  Contents Fish List Books
Ordering Gift Certificates Talk to us
Articles Photo Gallery  Shop Directory

 Jonah's Aquarium,
Email -