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Goldfish Glossary - A list of commonly used terms.

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Though some Goldfish breeds are delecate, Common goldfish are actually very hardy which is why they make such good pets. They can survive in outdoor ponds (even at tempratures which freeze the surface) and will eat almost anything.

However goldfish are also far messier than tropical fish, and produce a lot more waste. They only have an intestinal tract, without a stomach. So they cant digest excess proteins, and instead excreet it back into the water. This is a problem that needs to be addressed either with heavy filtering, frequent water changes, or both. If this is not done, they will eventually pollute their own water to the point where it is toxic, and they will die.


In general, water should be clear. But it is not an absolute indicator of how good the water is for your fish. Cloudy water can still be fine, and crystal clear water can still be toxic.

  Water Changes

Water changes are the process of removing water from the aquarium and replacing it with fresh tap water. Always remember to dechlorinate water. Dechlorinator (also commonly called "water conditioner") is cheap and is sold at virtually all pet stores.

Most tap water is chlorinated, because the chlorine kills bacteria and parasites. Some people believe you can dechlorinate water simply by letting it sit for 48 hours and letting the Chlorine evaporate, but that is not entirely true. Even after that process, there will still be chemicals remaining in the water that do not evaporate and can damage your fish. Water conditioner will completely nullify these chemicals in addition to the Chlorine.

Water changes are never bad for your fish. You can do them every day. But with proper filtration (and assuming your tank isnt overpopulated), you can reduce the frequency of water changes to once or twice a month. Changing 20% to 50% of the water volume is good. Changing more than 50% of the water should be avoided unless absolutely necessary to avoid stressing the fish.

Changing the water will instantly oxygenate the tank and will instantly remove pollutants such as ammonia. So in an emergency there is nothing that will correct water chemistry problems faster than a water change.

Do not forget to use water conditioner on the new water (any water going into your tank needs to be dechlorinated), and if you use aquarium salt, that will need to be (proportionally) replenished as well. You should make an effort to make sure the water is the same approximate temperature as the water in your tank to avoid stressing the fish as well.


People often assume that Goldfish thrive in cold water because they are often referred to as Cold Water fish. It is true that they can tolerate temperatures as low as 30F degrees. Common goldfish can even weather periods where ponds are frozen over, so long as they have enough oxygen and food. But warmer temperatures are healthier because warm water is less hospitable to parasites and bacteria. The ideal temprature of the tank should be in the 72F to 85F degree range, and they can tolerate temperatures to as high as 90F. Common aquarium heaters sold for tropical fish tanks will work just fine for Goldfish as well.

Warmer water holds less oxygen however, so fewer fish should be kept in warm tanks (or additional effort taken to increase oxygen, such as surface agitation or airstones). Temperatures above 90 degrees run the risk of overheating and killing the fish, so if you live in a very warm area, you will need to take care to cool down the aquarium.

Temperature changes should be gradual so as not to stress the fish. All aquariums should have a thermometer so you can track the temperature. Most pet stores sell adhesive strips that you can stick on the outside of the tank that are very cheap (under $2) and unobtrusive.

New fish should be acclimated to the water temperature before putting them into the tank. Float the bag on the surface of the water for 15 or 20 mintues before putting them into the tank. Dumping a new fish into the tank will stress it and increase the possibility of illness or death.

Keep in mind that a stable temperature will discourage breeding behavior. So if you want to breed them, you need to mimic conditions in nature; starting from a cold period and gradually warming. See the breeding section for more information.


Ph measures how acidic or alkaline your water is. Above 7 is considered alkaline. Below 7 is considered acidic. 7 to 7.2 is considered neutral. Goldfish prefer a neutral to slightly high pH. A pH of 7.4 is considered ideal for goldfish.

The terms "Hard" and "Soft" are commonly associated with pH, but are not the same thing. "Hard" water is water that contains a lot of minerals. "Soft" water is water with an absence of minerals. Soft water is often acidic, and hard water is usually alkaline. But the terms are not interchangable.

The pH scale is logarithmic...so a pH of 5.5 is ten times as acidic as a pH of 6.5. This is important in that the more radically the pH changes, the more it will stress your fish. If the pH changes by more than 0.3 per day, it will stress your fish. Stable pH is more important than ideal pH.

The pH will affect many bodily functions of the fish, including how it breathes. pH that is too low or too high can chemically "burn" the fish, causing damage to it's eyes, gills, or skin. Even if it is not lethal, it can cause stress. pH can also affect the fish indirectly...for example, ammonia becomes progressively more toxic as the pH of the water increases. The ammonia in water with a pH of 8 is far more toxic than the exact same amount of ammonia in water with a pH of 6.

Fortunately, goldfish have a fairly wide pH range they can tolerate, so this is not typically an issue for Goldfish. The "normal" range for most goldfish is between 6.5 and 7.5, which is also the range where most tap water in north America falls into. Goldfish can tolerate levels as high as 8, and as low as 6.

Water below 6 is too acidic, and could cause blood in the fins, excess slime, and loss of appetite. Water that is above 8 is considered too hard, and can result in a loss of appetite as well, and piping behavior (gasping at the surface). The harder the water, the less tolerance your goldfish will have for ammonia levels. At a pH of 7, goldfish can toelrate levels as high as 4ppm...but at a pH of 8, they can only tolerate up to .5ppm.

Water can be made more alkaline or made more acidic by way of chemicals that you can buy at most pet stores. Read the instructions and be very careful when altering your water pH. Carbon Dioxide and high water temperatures will tend to make water more acidic (lower the pH). Adding decaying organic matter to the tank (such as having water flow over peat, or adding driftwood) will also lower pH. Oxygenated water will tend to be higher pH. Adding minerals to the water like limestone or coral will raise pH.

Be aware that the importance of pH is often exaggerated. A stable pH is more important than maintaining it in the ideal range for Goldfish. The process of altering the pH of your tank is likely to stress the fish more than the fact that it is not in the ideal range. The general consensus seems to be that altering the pH of your water is more trouble than it is worth. So you should only alter the pH if it is absolutely necessary.


Aquarium Salt comes in cartons like this
In nature, Freshwater is not the same as what comes out of your tap. Tap water is truely salt free, but most freshwater is not. So a "freshwater" aquarium can contain small amounts of salt and still be considered fresh water. For this reason, many supposed "freshwater" fish will still tolerate moderate amounts of salt in the water, and some even require it.

Goldfish dont absolutely require salt in their water, but it does enhance their immune systems by stimulating them to produce more mucus over their scales (often referred to as their "slime coat"). Goldfish are supposed to be slimy. This is normal and desirable. Salt will enhance gill function as well (allowing fish to absorb oxygen a little better) and reduces the rate of nitrite buildup in the tank.

In addition, salt is toxic to many parasites that infect goldfish (including Ick, the most common parasite). So a salt environment will augment their immune systems in this way as well. Higher concentrations of salt are used as "salt baths" to immerse sick fish in for short periods. Salt is known to protect goldfish against nitrite poisoning as well.

  Salt Tolerance of Other Fish

Goldfish can tolerate low levels of salt. Almost all freshwater fish can tolerate salt to some degree. But be aware that some freshwater fish do not tolerate salt well at all, so make sure you dont have any of these fish in your tank and do not plan on adding them. They include tetras, catfish (including plecos/suckerfish), loaches, and any scaleless freshwater fish (though the consensus seems to be that you shouldnt mix goldfish with tropical fish anyway, salt or no salt). Snails are also not crazy about salt water, but some freshwater snails can endure the amounts you will use in a goldfish tank.

  Be Sure to Use Only Aquarium Salt

Do not use regular table salt. Table salt has Iodine, which is poisonous to fish. You can use Kosher salt but its best to remove all doubt and just use Aquarium Salt from a pet store that is specifically marketed for pet freshwater fish. "Aquarium Salt" is not the same product as "Marine Salt", which has additional stuff in it like calcium that marine fish require. The extra stuff in the Marine Salt may alter you water chemistry in ways you dont want. Marine salt is used for Salt water aquariums. Aquarium salt is used for freshwater aquariums.

Always fully dissolve salt before adding it to the tank. Undissolved salt can chemically burn your fish. Hot water will dissolve salt more rapidly, as will agitation.

The normal amount of salt for a freshwater aquarium is one rounded tablespoon per five gallons of water volume (there are three teaspoons in a tablespoon, and two tablespoons equals one ounce). But follow the directions on the box. To avoid stressing your fish, add the recommended amount of salt slowly (1/4 normal amount per day for four days).

A low concentration of salt is 0.1% (1 teaspoon per gallon). A medium concentration is between 0.1% and 0.5% (5 teaspoons per gallon). A high concentration is 0.9% (9 teaspoons per gallon) or above.

High concentrations should only be used for very short term treatment for sickness. Medium concentrations are dangerous in the long term and could kill your live plants as well. 0.3% (one tablespoon per gallon) is the maximum amount of salt that is safe for goldfish in the long term.

  Keep Track of the Salt in Your Tank

You must keep track of how much salt is in your aquarium. The only way to remove salt is through water changes. Salt should be fully dissovled before being added to the tank. If you lose track of how much salt is in your aquarium, begin doing a series of 50% water changes (once a day) for at least three days (a week is better). Then begin introducing salt again as if it were fresh water.

  Regarding Evaporation

To avoid accidentally putting too much salt in your aquarium, make sure you top off the water in your tank BEFORE you do water changes. Adding water does not remove salt from the tank, it only dilutes it. If the water level is consistend whenever you remove water from the aquarium, then you never have to worry about accidentally adding too much salt.

Replace salt in the new water (proportionally) before putting it into the tank. Once the fish are already acclimated to salt water, you dont have to worry about putting it in slowly anymore.


This chart illustrates how waste is processed by your biological figure. Click on the image to view a larger version.

This refers to the bacteria that naturally live in your aquarium. You dont have to put these in; they come in your fish and populate your tank by themselves. They exist pretty much everywhere in nature except in your tap water (because it is chlorinated).

The function of these bacteria in your aquarium is to neutralize waste products in the water produced by the fish, thereby reducing the overall frequency of water changes. Your biological filter will not remove the need for water changes completely, it will just reduce how often you need to do them.

Nitrification (Aka "Biological Cycle", "Start up cycle", "Nitrogen Cycle", or "Cycling") is the process by which beneficial colonies of bacteria establish themselves in a new tank. They come with your fish (so the process cannot start until you actually put fish in the tank), but it takes a period of time before they can replicate themselves sufficiently to function as a filter. And they will need a source of ammonia (such as a fish and it's poop) in order to grow. You'll never actually see them...they are very small. But they are there.

It is possible to cycle a tank without using any fish (by way of adding ammonia yourself) but the process is involved and complicated. Pet stores sell what amounts to fully cycled water in order to "jump start" the process. But the best method is probably to use living fish and plants.

Be aware that Chlorine will kill  these bacteria. So if you are washing places where they live (filter pads, gravel, ect...) you need to make sure that the water you use is already dechlorinated. These bacteria live everywhere in your aquarium, but the biggest concentrations will be where there is moving water. Like your filter (and any media in your filter) or the gravel (if you have an undergravel filter). Most power filters contain filter media with the sole purpose of providing a home for these bacteria, so that you will not lose your biological  filter when you change filter pads.

Do not be fooled by crystal clear water; the fact that your tank looks clean does not mean it is not toxic to the fish. Unlike a lake or a river, an aquarium is a closed system. Waste products produced by your fish and from decaying food in the tank remain in the tank unless they are removed or neutralized.

This can be accomplished by frequent (daily) water changes, but for most people this is impractical. The alternative is a biological filter; using plants or colonies of benign bacteria to convert the waste for you, so you dont have to change the water as often.


When urine and feces decompose in the tank, ammonia is released. There are two types of ammonia, but only one is dangerous to fish. When talking about ammonia levels, this is the type of ammonia that is a concern. Any amount above 0ppm (zero parts per million) is toxic, but levels at 2ppm or more is dangerous. Ammonia levels typically begin rising the 3rd day after fish are introduced to the tank.

An Ammonia Test Kit

If you want to remove all doubt, you can buy a monitor strip from any pet store. These look similar to thermometors that suction-cup to the inside of your tank. They provide a real-time measure of how much ammonia is in the water at any given time. They work continuously, but need to be replaced every one or two months. They typically cost between $6 and $10 if you buy them individually. Pet stores also sell kits with replacement strips that will average out much cheaper.

The pH of your aquarium will affect the tolerable levels of ammonia in your aquarium. The higher the pH, the less ammonia your goldfish will be able to withstand. At a neutral pH (7.0) Goldfish can toelrate up to 4ppm...but at a pH of 8, they can only tolerate up to .5ppm. Fast growing live plants (like Hornwort) are good at consuming free ammonia in the aquarium. Foods high in protein will produce more ammonia when digested.


These are the first type of bacteria that live in the tank. They eat ammonia, but excrete Nitrites, which are also toxic to fish. Nitrite levels begin rising the first week after fish are introduced.


This is the second type of bacteria that live in your tank. They eat Nitrites and spit out Nitrates. Nitrates are also toxic to fish but to a lesser degree, and are harmless at low or moderate levels.

So the point of the biological filter is to convert substances which are very toxic to your fish into substances which are only mildly toxic. Water changes still need to be done to remove nitrates once they get too high, but because your fish have a much higher tolerance for them, water changes can be farther between. Live plants can further augment your biological filter, but have potential problems of their own (see the plant section in "Setup and Maintanence" for more info)

Kits to test for these chemicals are available at any pet store. The cycle is fully established between 2 and 6 weeks after the fish are first intruduced. The bacteria grow more slowly in cold water. So warmer water will accelerate the cycle.

  A Note on Changing Your Filter Media

The filter media in your power filter (if you have one) is where most of the bacteria live. When you throw this away, you killing off the bacteria, and they have to start over with the new media. When changing your filter media, keep in mind that your biological filter will be weakened until it can re-establish itself. For this reason, many commercial filters use separate media...one on which the bacteria grow (which is never changed) and one which is disposable and can be periodically replaced.


There are many species of undesirable pond snails that infest aquariums

Aside from their asthetic value, snails eat one of the true pests of an aquarium; algea.

That being said, moderate to high levels of algea will still reproduce faster than the snails can eat them, and you will still need to scape them off occasionally. Snails dont eat algea evenly either, so are only really effective at controlling low levels of algea. They do eat live plants as well, but not to a great degree. Any live plants that can withstand the constant pecking of goldfish will probably endure snails as well.

Most freshwater aquarium snails are from the species Marisa Cornuarietis (part of the family Ampullariidae...aka "Apple Snails"). Like goldfish, these have been bred into a variety of shapes and colors, but they are all the same species. Marisa Cornuarietis are not asexual, unlike some snails. So if you want them to reproduce, you'll need at least two.

An Apple snail

Their reproductive process involves laying a clutch of eggs outside the water (so they will need several inches of space above the water line). Their eggs vary from pale to bright orange and look vaguely like a teaspoon full of tapioca pudding clinging to the glass. They gestate in about a month. The eggs need to stay moist but cannot be submerged, or the young will drown.

The other type of snail common to freshwater aquariums is the pond snail. This is a generic term that covers several species of snails that are considered pests. These are asexual, and a single one of them can quickly pollute your tank with dozens more just like it in a very short time.

They are generally undesirable because they are so small; they are not asthetically pleasing and dont eat algea very well. They tend not to last long in goldfish tanks though, because goldfish will eagarly eat them. For this reason, a lot of petstores will put a goldfish in with their tropical fish to eat any pond snails that are in the tank.

A Black Mystery Snail, a type of Apple Snail

Other snails should get along with most goldfish fine, although the goldfish may nip at them. For this reason you should keep snails that are big enough that they can weather this behavior (if they are about the size of the largest fish's head or larger, they should do fine). Most goldfish will ignore snails that are too large for them to swallow whole.

Where water conditions are concerned, they should be able to survive in any environment that goldfish can survive in. The general consensus seems to be that aquarium salt is bad for snails, but they can endure the low concentrations found in freshwater tanks. There is a website called Applesnail.Net that has more in-depth information about Apple Snails.


Goldfish are omnivores, and will eat anything they can fit into their mouths. They originated as bottom feeders (similar to catfish) and prefer foods that sink to the bottom or float in the middle, but can eat common flake food on a daily basis. The only reason floating foods arent great for them is because it forces them to swallow air while feeding.

  What To Feed Them

As a staple food, the best food you can feed them is pellets. Most chain stores will sell pellet food of some kind. Pellet food is more nutritious than flake food, and does not easily decompose the way flake food does (so uneaten pellets wont pollute your tank). It will also enhance the color of your goldfish as well. Hikari is one of the major manufacturers of Goldfish-specific pellet food, but Koi pellet food will work just as well. just make sure the pellets are small enough that your goldfish can swallow them.

An example of Goldfish pellet food

Most owners also feed them live (or freeze dried) food such as blood worms or brine shrimp once a week as a supplement. These are very good for the fish because they are high in protien, but will cause digestive problems if given every day. Goldfish will be very happy to eat the live versions of these foods, but freeze dried versions remove the possibility of parasites infesting it. Live food sold at most pet stores is unlikely to have parasites, but with freeze dried foods the chances are almost zero.

The amount of protein they consume (including blood worms, brine shrimp, ect..) should be limited when possible. High protein foods stress their digestive systems. You can be more liberal feeding them fruits and vegetables. Since they contain less protein, they wont stress the fishs' digestive systems as much.

Yes, Goldfish can eat raw fruits and vegetables, and such food is actually good for them. The food should be cut small enough that they can eat it, though they can tear off pieces of more supple foods (like oranges). A lot of people put cut slices in the tank. The fish will graze on it like cattle. Typical foods include oranges (the vitamin C boosts their immune system), skinless peas (often used to treat digestive problems), and lettuce. Cut it in sections that are small enough that they can either swallow it whole or bite off chunks of it. Oranges (or other fruits containing citiric acid) should not significantly alter the water chemistry, but excess food should be removed from the tank once they are done feeding.

  How Often to Feed Them

Feed them as much as they can consume in a 5 minute period, and only feed them twice a day max. People often overestimate how much food to feed goldfish. You have to remember that goldfish are cold blooded, and are kept in an environment where they dont have to expend a lot of energy looking for food or avoiding predators. Feeding them once a day is plenty, and they will actually do fine being fed only a few times a week.

With fruits and vegtables, you can be a bit more liberal. These foods are not dense protein sources, and so are much easier on their digestive systems.

  Avoid Overfeeding

One reason people feed their goldfish so much is because they believe the fish are hungry. But goldfish are ALWAYS hungry. Goldfish are gluttons...they will literally eat until they explode. They are biologically programmed to eat continuously. In the wild, this is a good thing. In captivity, it is dangerous for them. At best, overfeeding them will result in lots of fecal matter which will decay quickly and pollute your aquarium with ammonia. At worst, overfeeding will eventually cause their intestinal tracts to rupture and they will die. So you have to be careful in how much they are fed, especially for smaller fish.

Keep the high-protein foods (like blood worms and shrimp) as a once or twice a week treat to augment their normal diet of flakes or pellets. Feed only once a day or every other day. A sign of overfeeding is a line of feces trailing from their cloaca. If you see this, you need to reduce the amount of food you are giving them. It is always better to underfeed than to overfeed.

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