Monday, March 5, 2007

Goldfish Care Sheet - Fancy Goldfish

10/26/2008 - Sections added for "Filter Maintenance And Cleaning", "PWC - Partial Water Changes" and "Goldfish Illness Diagnosis".

Using my own experiences with pond and aquarium goldfish... AND due to the numerous "good" websites that, in my opinion, are still advising UNDERSIZED tanks or just "10 gallons per goldfish" (which is far too little IMO and based on scientific and mathematical facts), I decided to do my own "Goldfish Care Sheet".

Other references are listed at the bottom of this article but I wanted to post this link to one of the best "articles" on goldfish care that I've found on the net,, which, on page 2, has, "...Its true that a 40-litre (~10G) aquarium can house two to four small goldfish for a while but they will not reach their full growth potential or be as healthy as they could be. To properly house goldfish, they (all types) need 75 square centimeters of surface area for every 2 centimeters of goldfish" (comparable to 75 square inches of surface area for every 2 inches of goldfish, so an 8" goldfish needs around 300 square inches of surface area... that's 15" x 20" of surface area per goldfish!). "That means 120 to 200 litres of water for every goldfish" (~30G to 50G per goldfish).

Here's another good article all about Fancy Goldfish, that came out recently (Sept. 2008) in PFK - Practical Fishkeeping Magazine - a very good UK based magazine.
(You may have to "Join" the site, which is free, to see this article but it's worth it and you can also subscribe to get the e-Newsletter so you can read other good articles every month for free)

Another reference used for this care sheet is my own older blog article, "New Rules/Guidelines To Replace The Fish-Killing One Inch Rule", which has this info, "...Medium Large Fish (including Fancy Goldfish) - 3 Gallons per adult size inch for fish 6" to 10" as adults. Minimum Tank Size - 48" to 80" long (6X to 8X longer than longest expected adult sized fish in the tank)..." and "...Large Fish (including Oscars, Common Pleco's, Comets and Common Goldfish) - 5 Gallons per adult size inch for fish over 10" as adults. Minimum Tank Size - 80" long and UP depending on expected adult size of fish using the basis of 8X longer than the longest expected adult sized fish in the tank...."

A round-bodied goldfish increases it's body mass by eight times for every time it doubles its length. So a 2" goldfish is equal to eight 1" goldfish. A 4" goldfish is equal to eight 2" goldfish (or 64 1" goldfish). A 6" to 8" round-bodied goldfish is equal to hundreds of 1" goldfish... so how in the world can a goldfish be kept in 10G's of water? Would you keep hundreds of 1" goldfish in a 10G tank? A 6" to 8" round-bodied goldfish is a eating/pooping machine and there is simply no logical way that they should be kept in 10G of water.

Utilizing these three things as my primary references, here is my...

MINIMUM TANK SIZE: 55G, four foot long tank for up to two round-bodied goldfish; 100G, six foot+ long tank for up to two long-bodied goldfish.



I read this formula several years ago and it has always stuck because it makes so much sense...

A round-bodied goldfish grows eight times in body mass for every time it doubles its length. So a 2" goldfish is equal in body mass to eight 1" goldfish. A four inch goldfish is equal in body mass to eight 2" goldfish or 64 one inch goldfish. An 8" goldfish is equal to hundreds of 1" goldfish.

This is why 10G per goldfish is not enough water... IMO. I know a lot of people do it and it's all over the internet but it just can't be done long term as it will cause stress, stunting, poor water quality and many other health issues, ultimately leading to an early death of the goldfish. The numbers simply do not work out. Technically, based solely on body mass and size, a single goldfish shouldn't even be in a 55G tank. They are equal to much more than 55 one inch fish so even the fish-killing "one inch rule" excludes them from fitting in a 55G tank but for starting out, a 55G does provide the proper amount of swimming, water volume and growing room to give them a chance at reaching full adult size. By then, you will love your BIG goldfish so much that you won't mind getting a much larger tank. Another reason for giving them adequate water volume is this "old" saying in the fish keeping hobby.... "Dilution is the solution to pollution", meaning that having your goldfish in a larger volume of water will dilute the ammonia and waste they put out to lower the polution percentage levels between PWC's (partial water changes).

FILTER MAINTENANCE AND CLEANING (<-- Click to get to my article on this topic) For Goldfish, I recommend large filter systems like canister filters or HOB/Power Filters that have large reservoirs for holding a lot of filter media. The small filter cartridges on many HOB's simply do not have enough filter media mass to handle the waste level from goldfish. A good HOB/Power Filter brand is the AquaClear by Hagen brand. They come with a large filter media reservoir, a large sponge block, filter floss pad and BioMax which is a good nitrifying bacteria media. Having the BioMax and the large mass of filter media gives you a chance to partially clean some of the filter media (never clean the BioMax) without causing your tank to go into a mini-cycle like what happens when changing a filter cartridge out completely on other brands. PWC's - PARTIAL WATER CHANGES -

Even if kept in a proper sized tank and not overstocked, weekly 25% PWC's should be done or at least strived for. This will be your first defense in keeping the gravel from being too heavily clogged with detritus and will also remove/dilute any DOC's (dissolved organic compounds) that are in the water column. PWC's will also replace the trace elements and minerals that are constantly being utilized by the fish, nitrifying bacteria, any plants, microscopic life forms in the tank, etc.


There's no need for me to re-type things that have been documented over and over on several good webpages. Here is one of the first places that I would look for Goldfish issues. It's up to date and that site is generally a good source of information except I disagree with their 10G per goldfish recommendation on their care sheet and we have publicly debated that issue but they refuse to update their care sheet.

If that page does not help you with your goldfish issue, check out the other good fish disease diagnosis pages that I have listed on my "Disease & Illness Diagnosis And Treatment" page.

(To be continued, but read over the reference links at the bottom of this page for additional information)


References: (THE BEST "article" on goldfish care that I've found on the internet! Recommends 30G to 50G per goldfish) (Another VERY GOOD article that was just published in Sept. 2008 in Practical Fishkeeping Magazine which recommends a minimum of 36" long, 20G tank for a single fancy goldfish... but also stating that is only for starting out and that a larger tank will be needed as the fish grows.) (VERY GOOD forum thread turned into an article recommending at least 20G for the first goldfish and 10G more for each additional goldfish (to start off with) which is still too little water volume for adult sized goldfish but slowly but surely, care sheets are raising their standards.) (Temporarily NOT a good link. The site is down now but hopefully will be back up one day. It was a VERY GOOD forum post on goldfish care recommends at least 20G for one goldfish and a 55G for 3-4 goldfish) (GOOD, except for 10G recommendation. This care sheet recommends 10G to 30G per goldfish, so not too bad and much of the other information is good) (GOOD, except I disagree with 5 goldfish in a 60G tank... maybe 3 would work with proper tank maintenance for long term success. This care sheet does not differentiate between long-bodied and round-bodied goldfish and long-bodied goldfish need larger tanks due to their size and swimming capabilities.) and (GOOD, except for mixed signals on how much water volume per goldfish. One link talks about 7-10G per goldfish and the other page says 10G per goldfish is no where near enough for long term success.) (GOOD, except for 10G recommendation. This care sheet recommends 10G "at least" which is low, IMO, but the rest of the information is very good) (FAIR... Mixed between very good and not so good info. The first page has an example of a 55G tank... VERY GOOD... but then some of the links from this page goes off into much smaller tanks but usually not less than a 10G) (POOR... Starts off talking about "a bowl or tank" but later says 10G to 20G at full size which is still too little... NOT much "other" good info) (POOR... Starts off with a number of 2 gallons per fish inch... which isn't bad if they would have said "expected adult size" since that would have been 16G to 30G... but it didn't, so it's very misleading) (VERY BAD... starts off talking about "a bowl" and then says "2 gallons per goldfish") (VERY BAD... actually a copy of the care sheet above) (My own article on "NEW Rules/Guidelines To Replace The Fish-Killing 1" Per Gallon Rule")


  1. Just checking your math in paragraph 2:

    The cited reference article does indeed say 75 square centimeters per 2 centimeters of fish. But this is equal to 11.625 square inches per 0.787 inches of fish, or about 15 square inches per inch of fish. Therefore an 8" goldfish would need only 120 square inches of surface area, not 600.

    Generally the limiter is volume, not surface area - I've found that if you go with a reasonable volume figure any standard-size tank will have far more surface area than you need.

  2. Yep. You are correct that I made a typo on the math.

    I need to re-read that article though. In the same paragraph where she mentions the 75 per 2 cm measurement, she also says 120 ltr to 200 ltr per goldfish (30G to 50G) so the 120 square inches cannot be correct since that would only be 10" x 12" of surface area which would have to be 60" deep to get up to 30G of water volume. I didn't check the metric to standard math conversion, which I should have done. My Bad!!!

    I simply transposed inches for centimeters to come up with my figure of 600 square inches which was also an error. It should have been 300 square inches using "my" non-math. But thanks to your pointing out the error in the math, I'll be correcting the original article after checking things out with the author of the linked article. I'm thinking there is a typo in her article to where the 75 square cm to 2 cm of goldfish should have been more related to body mass, rather than length, so maybe it should have been 75 square cm of surface per 2 square cm of body mass.

    I'll update the article when I have more definitive information. Until then, I'll stand by my 20-30G per fancy goldfish as a bare minimum with a 55G 4' long tank size as the bare minimum tank size.

    Anything smaller will lead to long term health and stunting issues.


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