| Home | Back to Background Information | Back to Goldfish |
~ FOR KEEPING HEALTHY GOLDFISH ~
Background to fish health
Generally speaking, fish live with a low-level infection of various bacteria
and parasites all the time, and the fishes' immune system suppresses any problems
of infection that arise. If a fish's immune system is stressed, then infections
and parasites are given an opportunity to develop and start to cause health
problems, which further stress the fish, and so things worsen.
The commonest cause of stress is poor environment, especially poor water quality.
In some cases, infections and/or parasites are introduced into aquaria with
new fish or plants that have not been quarantined properly. Generally, over
90% of disease problems are due to poor water quality, with less than 10% being
due to introduced diseases/parasites or other causes; poor water quality means
insufficient dissolved oxygen due to overstocking and/or too many organic wastes.
Understanding the above is the key to successful fishkeeping. Here,
then, is some 'off-the-shelf' general advice on goldfish keeping; we hope it
Buy a book!
First, if you haven't got one already, quickly go out and buy a basic book
on goldfish keeping - such as the Interpet Guide to Fancy Goldfishes by Dr Chris
Andrews, about £6 - and get reading. (Chris Andrews ran the London Zoo
aquarium and now runs the US National Aquarium in Baltimore). (The cost of the
book will save much of the cost of ignorance of the rules).
The four fundamentals
These are the four fundamental things to get right:
- stocking level
- water changes
Stocking level - what are the SURFACE dimensions (length x width) of your tank?
As a guide, in a coldwater aquarium, you should allow:
- 60 square cm for each 1 cm of fish body length excluding the tail
- 24 square inches for each 1 inch of fish body length excluding the tail.
For example, in a 60 x 30 cm (24 x 12 inch) tank you can keep a total of 30
cm (12 inches) of combined fish body length, such as three 10 cm-long fishes
(three fish each 4 inches long), or two 15 cm-long fishes (two fish each 6 inches
There is no way round this! If you overstock, you will always be up
against problems; remember, too, that small goldfish grow, so you need some
spare capacity for growth of your existing stock. Do your sums, and, if you
are overstocked, find temporary accommodation for your surplus fish until you
either get a second or a larger tank.
See our aquarium calculator to help you determine safe stocking levels and for further advice on this subject.
Filtration - goldfish produce a lot of waste and as a general rule undergravel
filtration cannot cope with it. There is no way round this! If you have
just an undergravel filter, leave it in place and running but buy an internal
power filter or an exterior canister filter as well (Interpet, Tetra, Eheim,
Fluval, etc - tell the retailer your tank dimensions and he/she should offer
you the correct model). You could also buy a filter bacteria culture (sold in
plastic bottles by Hagen, etc) to start the new filter off. If you have an undergravel
filter, you must also have an air pump to be running it - good, as this provides
The commonest aquarium problem is inadequate biological filtration on account
- new tank syndrome (i.e. tank stocked too quickly, before the nitrogen cycle
(see below) has become established),
- insufficient filter capacity (either too many fish in the tank or too small
- poor filter maintenance.
Not having a filter at all means you must rely entirely upon frequent, large
water changes (see below) for the health of your fish.
Feeding - if you have a water quality problem, stop feeding until the problem
is over, to reduce the level of wastes in the water. Then resume feeding very
lightly: two or three small feeds every day are better than one larger feed
as there is less uneaten food and the fish then scour the bottom for leftovers;
any food not eaten up in two or three minutes is too much. (Goldfish can go
for up to two weeks without food - for example, when you go on holiday, it can
be safer to leave fish unfed rather than risk a neighbour overfeeding them and
polluting the tank).
Feed a good flake food such as Aquarian or Tetra goldfish flake daily. Supplement
flake with live or frozen foods (frozen is just as good, and easier!) no more
than once per day for four or five days per week. Overfeeding is the commonest
mistake in fishkeeping, according to numerous surveys. In fact, one or two days
per week without feeding anything at all can help towards better water quality.
Water changes - if you have a water quality problem, change 50% of the tank
water every day until the level of nitrate (see below) drops to about 25 ml
per litre (yellow on the test kit scale, if you are using a Tetra test kit),
and thereafter change 25% per week every week. Use a dechlorinator (Tetra,
Waterlife, etc) to treat tapwater, to remove the chlorine/chloramine (put in
by the water authority to disinfect the water, to make it safe for human consumption)
and any dissolved heavy metals.
Fish excrete ammonia (their equivalent of urine) via the gills into the water,
which is invisible and toxic - so clear water does not necessarily mean safe
water. Filter bacteria then convert ammonia to nitrite then nitrate (this being
known as the nitrogen cycle), and the fishkeeper must remove the nitrate - there
is no way round this, too!
There are three ways of removing nitrate:
- water changes,
- technical means, and
- a healthy growth of plants to utilize some of the nitrate (which is a plant
Rely on water changes, with good plant growth as an extra if you can achieve
it; technical means include chemical resins (placed in a nylon bag in your filter)
to absorb nitrate, and de-nitrating filters - both are expensive and can go
Always clean the internal/canister filter media (foam pads, filter wool, etc)
in a bucket with water taken from the tank, as water straight from the tap will
kill the filter bacteria (because of chlorine). The goldfish book will have
diagrams and charts explaining all this if you are not familiar with it.
Seek good advice
Look around for a knowledgeable retailer and for a goldfish club, if you can.
It's worth subscribing to Practical Fishkeeping Magazine (or overseas equivalent!)
to keep up to date with advances in fishkeeping techniques.
© Bristol Aquarists' Society