Welcome to the GSGB’s Frequently Asked Questions page.  Here we have brought together some frequency asked questions we receive from members and non-members alike regarding fishkeeping and compiled our answers.

You may find our answers are different from those you see on Forums.  There may be good reasons for that, not least of which is that several people with 30+years’ experience of Goldfish compiled these answers and we didn’t always agree!

In many regards there are no right answers.  Experience and the particular circumstances might alter the way to approach some things.  There is also much more that can be said about many of these topics but we aren’t writing a book and of course, membership of the GSGB gets you access to some of the most experienced breeders and keepers of Goldfish in the world!

Please feel free to contact us if you would like to know more about the benefits of membership.

Assuming that you have the aquarium illuminated, then probably the most appropriate time is 15 minutes after the lights have been switched on.  This gives the fish the time to wake up and become active and therefore looking for food.

In cases where new fish have been introduced, give them at least 24 hours and approach the question based on the illumination point above.

One of the most common problems experienced by those new to Goldfish (and sometimes those more experienced as well) are those of poor water quality. The causes are almost always a combination of one or more of the following:
• Too many fish for the space
• Too much food
• Too few water changes
• Inadequate filtration
All fish produce ammonia either excreted directly from the gills or from the break down of solid excrement. Ammonia is poisonous to all fish but thankfully “friendly” bacteria will break it down and convert it to Nitrite. Sadly, nitrite is also poisonous to fish but again other “friendly” bacteria can break it down to Nitrate, which except in very high concentrations, is not poisonous to Goldfish. This transformation is known as the nitrogen cycle. It takes time and effort to prepare the filter – to get the “friendly” bacteria in sufficient numbers in the filter to process the amount of ammonia or nitrite present.
The volume of bacteria necessary will vary as new fish are added / the feeding increases / the fish grow so sudden changes in these parameters can through the bacteria supply and demand out of balance.
You can condition a filter before you add the fish – the process is called “fishless cycling” and usually takes about a month. Fish food and starter kits commercially available are fed to the filter to build the process before introducing the fish. Please research fishless cycling and follow the process before you buy any fish. You can test the progress using the commercially available test kits. The dropper versions are generally more accurate than the test strips and buy your own kit. You need to see the results and test frequently. Using the local aquarium shop is likely to be much more expensive and you may not get the actual results. Keeping a record will also show you if things begin to change and enable you to take action earlier and to learn from past experience.
Therefore, the key to success is to ensure the ammonia and nitrite are “processed” quickly and nitrate is removed by, among other ways, water changes. Even with appropriate filtration, substantial water changes are still essential. About 50% per week (or better 25% twice a week) is probably a good rule of thumb but more is necessary if the filtration is not adequate.
Filters won’t be able to cope if there are too many fish for the water volume. So you need to think about the combination of biological filtration capacity, the frequency at which solid matters are removed from the filter, the number and size of the fish and the water volume. There are many opinions on this but so much depends on the experience of the fish-keeper, the time available and the size, as well as the number, of fish that it is not a simple statement of X litres of water per fish.
Excessive feeding is another common source of problems. Uneaten food decays and pollutes the water. Therefore it is essential that only enough food as can be eaten in a few minutes is provided at a time and no more than 2 or three times per day.

Goldfish can stand a wide temperature range – from near freezing to more than 30C – if the variation is gradual.  Even over a 24 hour period temperatures can move from say 23C to 30C and back again and this will be fine.  The problems come with sudden and extreme changes as the fish are cold blooded and therefore are suddenly operating at a completely different temperature from their surroundings and are shocked by the change.  A difference of half a degree or so Celsius is not too much of a problem but anything more, particularly for the round bodied varieties can be just such a shock.  For equalisation please see the FAQ on introducing new fish to an aquarium.

This is probably the most common health issue other than those caused by poor water quality.  The swim bladder is vulnerable to disruption (and therefore the fish to buoyancy issues) from a number of causes:

  • The most likely problem is genetic. The careful breeding of selected fish can significantly reduce the occurrence of the problem.  Buying fish from breeders rather than pet shops will help!  Before you buy, watch the fish carefully.  Is it swimming properly – controlling its position in the water?  If not, then don’t buy it.

  • Water quality can disrupt the fish, so maintaining clean water is crucial. Particularly high nitrate (so even if the filters are working, you must still complete regular substantial water changes).

  • Temperature changes – particularly sudden ones – can induce problems

  • Taking in air – perhaps through gulping it in with floating foods – can also cause problems

  • Eating foods that swell inside the body (so check the foods in a small amount of water to see if they swell significantly before feeding it to your fish)

Once the problem exists, then the choices are limited – warm, shallow clean water, good foods eg frozen bloodworm, might help.  However, if the problem is genetic then the prognosis is not good and if the problem isn’t corrected quickly, it is best to consider euthanasia rather than prolonging the problem and any suffering for the fish.

As we have discussed in “water condition”, the nitrogen cycle is crucial to the success of a filtered aquarium.  However, it takes time for the necessary, “friendly”, bacteria to populate the filter and thereby allow it to operate at the necessary performance.  Indeed if a filter is not prepared, then the introduction of fish and filter simultaneously must mean the production of ammonia exceeds the ability of the bacteria to process it and therefore the poisoning of the fish.  Apart from returning the fish to the supplier while you get the filter “up to speed” the only solution is very very large and regular water changes to avoid the fish being poisoned.  However, the very removal of the ammonia will inevitably slow the development of the filter.  The best way is to develop the filter in advance of acquiring the fish.  Fishless cycling is well discussed on the web and is explained in this site: www.    Once the filter is cycled and ready then of course you can introduce the first fish.  However, on the introduction of any more fish the ammonia production will be out of kilter with the capacity of the bacteria to process it.    Therefore at such times you need to be extra vigilant regarding ammonia or nitrite spikes that could harm your fish.

When it comes to changing filters, remember to remove the solid waste but retain the bacteria (by washing the media in tank water, not fresh where the chlorine will kill the bacteria) and only wash part of the filter each time – in rotation so you maintain a healthy bacteria population.

The best way to introduce new fish to an existing aquarium is to place the fish in a bucket of their quarantine tank water, then check that water and the water in the aquarium into which they are being moved are at the same temperature.  If they are not,  add main aquarium water to the bucket gradually until the temperatures are equalised.  Once they are, catch the fish and move it swiftly into the new home.  Make sure throughout that the aquarium lights are off and only turn them on the following day – so the fish get the opportunity to settle into their new home in a calm environment and not, literally, in the full glare of bright lights.

If you acquire new fish from any source, you should quarantine them before introducing them to your established stock. This applies whatever the source and whatever the outward appearance of the new fish and their prior housing.  This is because the fish may be carrying diseases that have yet to be visible or that the fish while healthy themselves may have been housed with sick fish (for example in a circulating system in a shop) or may simply find the move a shock which weakens them and allows a disease to take hold (including diseases the existing fish may carry but to which they are resistant).

The duration of the quarantine is always a subject of debate, though a month, at room temperature or preferably at about 22 – 25C, would be a good way to encourage the development of any disease the fish harbours.  Cooler water or shorter duration may mean problems are masked and not identified.

There is no need to treat the fish with anything during the quarantine period unless and until a problem is identified.  A sponge filter, a heater, an airstone and an otherwise bare tank is ideal.  The aquarium need only be large enough to house the fish for the duration.  You will need to complete water changes so remember to use different equipment to that you use for the existing stock.  Feed the fish sparingly but with a good quality pellet food once a day and watch the fish carefully.  All being well the fish will be fit and healthy and ready to introduce to the existing stock in a month.

If you are introducing new fish to an established aquarium, please see the FAQ on quarantine.

If you are introducing fish to a new aquarium, please see the FAQ on Water Condition.

Goldfish are carp and spend a lot of time sifting through materials on the bottom of their home looking for food.  If you use gravel it is essential the pieces are of the appropriate size.  Too large and food will get in between the pieces and can decay – polluting the water.  Too small and it will compact and can cause problems both for any rooted plants and can cause water quality problems if there is any biological material in there that decays.  Ideally the gravel will be about 2-3mm in size and of course, neutral regarding the effect it has on the water.  This size also works well for growing plants in the aquarium (assuming your Goldfish don’t uproot and / or eat them!).

Similarly, there are issues with the size of the gravel for the fish.  If they take the gravel into their mouths it might get stuck.  Removal is best done with tweezers but it is difficult and damaging the fish is a real risk.  It is much better to not have the problem by having the right size gravel to avoid the risk of it getting stuck.  Therefore gravel has to change as the fish grow.  In fact, it is generally better not to have gravel at all.  The fish will be fine, the water quality easier to maintain and the problem goes away.