guides & articles

Related listings

Latest Postings

Subscribe to the hottest news, latest promotions & discounts from STClassifieds & our partners

I agree to abide by STClassifieds Terms and Conditions

Self-Improvement & Hobbies

What’s a safe stocking level?

Less is more - ensure ample manoeuvring space for your fish by keeping to a safe number in your tank
CATS Classified In The Straits Times - February 26, 2011
By: James Ong
| More
What’s a safe stocking level?

You may love the idea of a tank packed with colourful fish swimming to and fro, but can the tank you have hold a lot of fish safely? How do you know how many fish you can keep in a tank without overcrowding them?

‘One inch per gallon’ rule

This popular rule gives only a rough estimate. Because fish are not all the same size and shape, a tank that can comfortably hold six inches of lithe and slender fish may not easily hold six inches of full-bodied creatures like goldfish. Full-bodied fish need more water to thrive in, both for reasons of space, and because they generate more waste matter.

Remember also to use the adult size of the fish in your calculations. A fish that is tiny when you first bring it home could rapidly grow to several inches in length.

Also, do not use only a tank’s dimensions to calculate the number of gallons of water it will hold. A tank filled with gravel, rocks, plants, and an assortment of decorations is going to hold less water than its length multiplied by the width and height would suggest.

Surface area calculation
More oxygen gets into the water when more of the water’s surface area is exposed to the air.  A tank with a larger surface area therefore can support more fish. A tall, thin tank may contain the same amount of water as a short, wide tank, but their very different surface areas mean that they cannot hold the same number of fish.

Surface area is calculated by multiplying the tank’s width and length. According to the water surface area rule, you can have one inch of fish for every 12 square inches of surface area. But remember that slender and full-bodied fish differ in their needs, so you cannot blindly follow this rule either – make the calculation far more generous for bigger-bodied species.

Which calculation to use?
If your fish are slim and relatively small, and the tank you have is of a regular shape and size with a good surface area, the “one inch per gallon” rule holds reasonably true. But if you have an odd-shaped tank, and big-sized fish, it is safer to go with the surface area rule.

When in doubt, you should under-stock your tank rather than risk exceeding the safe limit.

A little at a time

Even when you are happy with your calculations, and have determined that you can keep 20 of the fish you want in the tank you own, don’t go out and get all 20 fish at the same time.

Be patient and get five out of the 20 first. Let them adjust at the same time as colonies of beneficial bacteria in the tank adjust to the work they will have to do breaking down the toxins in the fish’s waste matter into more harmless substances.

When the aquarium is doing fine, introduce a few more fish, wait a while, then add a few more, until you reach the correct number. Remember also to quarantine new fish in a separate tank for a couple of weeks so you can check that they do not have any diseases they may spread to your current, healthy fish.


Pop! Goes the music - Drums