Goldfish Care

4. Why is the water in my tank cloudy?

If you just filled the tank with water, the cloudiness may be very small bubbles that will dissipate over an hour or so. If it is an aquarium that you have recently setup (say the first week), then this is a normal thing that is commonly attributed to a proliferation of bacteria. It is not harmful and will go away as the tank’s ecology settles down. However, take it as a warning that you need to monitor the water quality and possibly do very frequent water changes until the biofiltration is established.

If your tank is well established, then this may be the start of an algae bloom in the water (particularly if there is a yellowish tint to the water). Read the discussion of plants elsewhere on this site, and about how to control algae. These blooms tend to come and go somewhat inexplicably.

It also could be the simplest cause of all; your fish food is clouding the water. Put some in a glass of water and stir lightly. If the water is left cloudy and it stays that way for hours, you could have the source of the problem.

5. How do I know when I need to change the water?

I’ve spoken to a number of very experienced hobbyists (30+ years of experience) who say they know when to change water by looking at the fish. They "cut their teeth" before the availability of water quality test kits, so they had to develop this skill. The downside of such an approach is that you will kill a lot of fish learning what works (they all did). It’s not that your fish will all spontaneously combust if you do it wrong. Rather, you will have continuous small problems all the time that you may or may not realize are due to water quality.

I tend to be a very quantitative hobbyist. I make extensive use of test kits to calibrate myself to what care a given set of fish in a particular tank need. I typically change water when the nitrate level is between 20 and 30 mg/l (or ppm). This is for established tanks; for a tank that is "cycling" (developing the bacterial cultures that perform biofiltration), I change enough water to keep the ammonia below 1.0 ppm and the nitrites well below 0.5ppm.

6. How do I change the water?

This depends on the tank size and the amount of water you change. It also depends on your water. Why the water? Because some water does not have good characteristics when it first comes from the tap. Well water can be very low in oxygen and needs to be aerated overnight, before going into an aquarium in any significant quantity. Well water and some municipal waters can often have unstable pH also, usually due to significant dissolved carbon dioxide. Water in the Chicago area, for example, comes out of the tap at a little over pH 7.0, but then rises to over 8.0. Goldfish can survive quite well in almost any pH, but they can be harmed by sudden changes of more than a few tenths.

So test your tap water, to make sure it does not need any special aging: test pH right from the tap, then aerate in a bucket overnight and test again.

Assuming there is nothing complex about your water, you will do changes using a water changing device or with buckets. For small tanks, two 5 gallon buckets will do the job. Use one to store fresh, dechlorinated water of the same temperature as the tank. Use the second to siphon old water into.

The water changers are tubing arrangements that hook up to a faucet. They can be wasteful of water, but are very much simpler than carrying buckets. Follow the manufacturer’s instructions.

For big tanks (say 40 gallons and above), I use a bucket and hoses. I siphon some tank water into a bucket, catch the fish by hand and put them into the bucket. Then I turn off the filter, siphon out the tank, and refill directly by hose from the faucet. I add the dechlorinator directly to the tank as the water is going in. Make sure the temperature is the same as the bucket water. I usually leave the tank to settle down for 20 minutes or so, then turn on the filter and put the fish back in.

7. Should I try to adjust the pH of my water?

No. I have successfully kept goldfish in pH 6.5 and pH 8.5 water. Your life will be wretched unless you get your fish used to the natural pH of your water. The main problem is that pH adjustments tend initially not to be stable; the pH bounces back towards the original pH after adjustment, requiring multiple treatments. Goldfish should not be subjected to this.

8. I read about the size of tank and filter that you say goldfish need, but I can only afford/only have room for the bowl I got. Is this okay?

Of course not. For the same reason you shouldn’t get a horse if you live in a one bedroom apartment, you shouldn’t get a goldfish if you can’t provide a suitable habitat for it.

9. Can I keep my goldfish small by keeping them in a small tank?

Yes. Small and short-lived. A goldfish should live about 7 to 10 years; fish kept in small tanks or bowls rarely live more than 2 or 3 years. On average, they only live a couple of days (for every fish that makes it to 3 years, there are thousands that died the first week).

10. Why don't you like charcoal in your filters?

I have nothing against activated charcoal. However, I change 100% of my tank water weekly. Charcoal gives no benefit unless it is at least as clean as the water. So I would need to change it weekly. Except for special cases, then, I usually don’t bother with it.

11. Why don't you like canister filters?

The one I have is too much trouble to clean. Having equipment that is easy to maintain is very important; otherwise maintenance may not get done. Others seem to like canister filters, though, so make your own judgement.

12. My goldfish tank in my house gets too warm in the summer; what can I do?

Basics: make sure it is not in direct sun and raise any lights up off the tank so that they do not heat the water. If the temperature is still high (say in the 80 to 90F range), then consider getting a fan. Place the fan so that the air blows across the tank’s water surface. The resulting evaporative cooling can lower the temperature very quickly. Be careful! Goldfish don’t like fast temperature changes, particularly towards cooler temperatures.

13. What other fish or animals can I keep with my goldfish?

None. Turtles and pleco-type catfish will (eventually) attack goldfish, nipping fins or sucking at the slime coating. Small corydoras catfish need higher temperatures than goldfish like, and can be swallowed by larger goldfish, resulting in the goldfish choking to death. Snails can carry parasites that are harmful to goldfish. Koi carp are too boisterous, large, and aggressive for all but the fastest single-finned goldfish to coexist with. And so on; there is really some sort of problem with keeping anything but goldfish with goldfish.

I have to laugh when people ask me about those cute little aquatic Clawed Frogs. Granted, when they are an inch long, they are not much of a problem. But when the one I had reached 6-inches, it was eating 25 goldfish a week!

14. Why would the pet shop sell me a bowl if it weren't the right thing to keep goldfish in?

The charitable answer is that there is a consumer stereotype that goldfish live in bowls and that pet shops get tired of trying to argue with customers and educate them that this is not the best way to keep goldfish.

The uncharitable answer is that they don’t know any better and if they do, they can’t afford to lose the sale, which is what would happen 9 out of 10 times, if they tried to sell you what you really needed. Think about it. You come in to buy a $0.25 goldfish, and the pet shop tells you that you need a $15 filter, a $15 aquarium, lights, test kits, a siphon, and other stuff probably totaling $50. The average customer will think they are being taken advantage of, especially when, there, sitting on the shelf, is the T*tra complete goldfish bowl kit for $6.

Let’s say you just won a fish at a fair and want to do this cheap. Get a garbage can made of plastic number 2 (HDPE) in a 30-40 gallon size (about $8 from a place like Walmart). Put it outside where it gets some sun, fill it with dechlorinated water, and toss the fish in. Feed the fish sparingly twice a week. That’s it.

15. Why would the pet shop sell me 10 goldfish if that were too many for the tank they also sold me?

Because you wanted 10 fish and they are there to sell fish. It would have taken a lot more effort to convince you to buy just 2. And it probably would have gotten the sales clerk who helped you fired. It’s like saying "why do supermarkets sell ice cream to overweight people?".

16. Your web page says to do (something), but the pet shop says this is wrong and I should do (something else). Who should I believe?

First off, please don’t send me a note like this. Resolve the dilemma yourself. This kind of thing puts me in a bad mood for the whole day.

The advice on this page meets two criteria: (1) it works for me and (2) it will keep the broadest audience possible out of trouble. This doesn’t mean that completely different approaches will not yield good results in certain situations. If the pet shop’s advice seems to make sense because of some special circumstance, then maybe it is better advice than mine.

If the shop is willing to back up their advice with any sort of a guarantee, like a full refund if the fish dies after you followed their instructions, then I would do what they say. But if they don’t, then caveat emptor!

You should recognize that the pet shop faces the fundamental problem of staying in business, which is no small challenge, especially for the few independents left who have knowledgeable staff. If you come in with fin rot, as an example, they can spend 20 minutes explaining to you how adding salt to the water and doing frequent water changes can cure it (and make no sale for the effort). Or they can spend 2 minutes to sell you $5 worth of antibiotics. And since the antibiotics will only treat the symptom (bacterial fin rot) and not the underlying problem (stress due to poor water quality), you will be a repeat customer for fish and medications.

17. I've read through your web site and recommendations, but I have had twelve fish in a 20 gallon tank for 3 months with no problems (variant: I have had a fish in a 2 gallon bowl for 3 years). So I think you are nutty. Are you?

I am certainly nutty. I have a basement full of tanks of goldfish. And I have to answer questions like this.

This site is dedicated to long-term success with goldfish. I define long-term as "years". Some people, through luck, exceptionally tough goldfish, or some special factor, can defy the most basic guidance on this site and still have success. If the reason is luck, then it usually runs out. I have many notes from people who didn’t quarantine their fish, or never vacuumed their gravel, or only changed water once a month, and then eventually had catastrophic problems … usually a bacterial disease epidemic too rapid to diagnose and treat.

I will note that I tried to keep goldfish back in the 1970’s, and had no success at all. I knew none of the information on this page. Through associating with serious, long-term hobbyists, I have reached the conclusions that I relate on this site as information and advice. I would urge you to start right and then experiment with varying the care parameters. Don’t start looking for trouble.