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Stocking Guidelines and General Advice
Published by Fishy-Fishy on 28/11/2006 (28563 reads)
Room for One More? Fk member Fishy-Fishy explains stocking levels.

Room for One More?

Stocking Guidelines and General Advice

Why stocking levels are important

A massive number of fish illnesses are caused by poor water quality so keeping your aquarium and its water in good condition is your main priority. If you have too many fish for your aquarium then the water quality will be difficult to maintain, meaning illnesses for your fish and a massive headache for you! It?s better to start out right by researching and planning the size and number of fish you can have as this will help prevent many problems in the future.

Common mistakes

The most common mistake that people make when stocking their aquarium is to assume that the fish available in aquatic stores are fully grown. This is not the case and so when the fish grow to their adult sizes, fishkeepers are often left with massively overstocked tanks, or worse, a tankbuster that they cannot house properly. To prevent this from happening, you should always always research the fish you are planning to buy. Remember to ask for the fish?s Latin name to prevent any confusion over common names which can vary considerably.

Another thing to bear in mind is livebearers, that is guppies, swordtails etc- if you have them then you will know that the breed like crazy! Make sure you have somewhere to rehome the fry so that you don?t get overrun. Consider having a female-only shoal if you think you won?t be able to rehome any fry.

These are general guidelines and are no substitute for a regular water testing regime!!


General guideline- 1" of fish per gallon (2.5cm per 4.5 litres)

Goldfish- the more space they have the better! A tank of around 30 gallons would be big enough for 1 fancy goldfish. Each additional goldfish should be allowed an extra 10 gallons. Goldfish grow to at least 6 inches so need a lot of swimming space. A 3 foot long tank is the smallest tank you should consider for fully grown goldfish.

Young goldfish can be safely kept in a smaller tank but will need to be moved to a larger tank or pond as they grow.


General guideline- 1" of fish per gallon (2.5cm per 4.5 litres), this can be built up gradually to a maximum of 2" of fish per gallon (5cm per 4.5 litres) depending on filtration

You should start by gradually building up to 1" of fish per gallon and then waiting until your fish grow a little. Keep a record of water tests so that you get an idea of how the system copes with the current load of fish, paying attention to how long it takes for the nitrate (NO3) to reach 50ppm and the number and size of water changes you need to do. Then it is up to your discretion to decide if your aquarium can cope with more fish. If in doubt, you can always ask us on the main forum!


General guideline- reef tanks- 1" of fish per 4 gallons (2.5 cm per 18 litres), fish only- 1" per 2 gallons (2.5cm per 9 litres)

Marine fish and inverts are more sensitive to nitrate, nitrite and ammonia than freshwater fish so you will need to allow more water per fish than in a freshwater aquarium. Some marine fish that are offered for sale as aquarium fish can grow very large, so don?t forget to research their adult size before you buy.


General guideline- 10" of fish per 100 gallons (25cms per 454 litres)

Some fish that are available for ponds can get very large so make sure you choose fish carefully- stick to goldfish if your pond is on the small side.

Be aware that your fish may multiply quite quickly so you should be prepared to rehome some fish in the event that your pond gets overcrowded.

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