If you are a first time fish owner, it can be very tempting to fill your tank with as many wonderful tropical fish as you can.

It is very important to keep your tank at least slightly understocked. Having too many fish will lead to illness, fighting and even death.

One of the biggest mistakes that people make with tropical fish is overcrowding their tank.

**As a general rule, the calculation for how many fish can go into your tank is 1 inch of adult fish per 1 gallon of water, making sure to take 10% of water off for gravel, decorations etc. Territorial species of fish will need double the space, so 1 inch of fish per 2 gallons of water.**

There are other things that need to be taken into consideration, which I will cover in this article.

**Things to Consider When Calculating How Many Fish can fit in your Tank.**

**Water Measurement.**

Depending on where in the world you are, your tank capacity will either be in gallons or litres.

In America, they use US gallons. A US gallon is different to an imperial gallon (just to complicate matters even more). 1 imperial gallon is the same as 1.2 US gallons.

In the UK, they use litres. 1 litre is the same as 0.3 US gallons, or 0.2 imperial gallons.

**There is a BIG difference between a litre and a gallon when it comes to the size of a fish tank. 1 litre is the equivalent of 0.3 US gallons.**

**Substrate, Plants and Decorations.**

As a general rule, you should take away at least 10% of the water in your calculation to account for any gravel, plants and ornaments. If you have many plants in your tank, I would up that to 15%, just to be on the safe side.

**Single Species or Community Tank?**

It is slightly more difficult to calculate space requirements if you have a community tank as some species of fish can be territorial so need double the amount of space.

Do your research on the different types of fish you would like to see what their temperament is like.

**Size** **and Shape.**

This is probably the most important thing to remember. You must do your calculations based on the **adult size of your fish**, not the size they are when you get them. You also have to consider the shape of the fish as an adult. Wide bodied fish need more space than narrow bodied fish.

Again, do your research to find out what the average adult size of your fish species will grow to before working out how many you can add to your tank.

**Future Proofing.**

When a Mummy fish and a Daddy fish love each other, they make many baby fish! If you are going to have males and females of the same species, you will end up with more fish. If you have stocked your tank up fully your tank will get very overcrowded very quickly once this starts happening.

**How Many Rainbowfish Can I Put into a Tank?**

When it comes to adding Rainbowfish to your tank, there a few things you need to consider.

In addition to having the correct sized tank for Rainbowfish, you also need to make sure you have the correct shape. Rainbowfish need space to swim around the middle and top of the tank, so need a large surface area to be able to do so. It is no good having a really tall but narrow tank as this will not give them the space they need.

It is easy to work out the surface area of a tank.

Surface area of a fish tank = length x width.

**To calculate how many fish you can have using this method is:**

**1 inch of adult fish for every 12 square inches of water surface area. For wide bodied fish, it is 1 inch of adult fish for every 20 square inches.**

**The greater the surface area of** **your tank, the more fish you should be able to have.**

Most Rainbowfish would be classed as wide bodied fish.

If your calculations don’t end up as a whole number, always round your number down to err on the side of caution.

There is a brilliant fish stocking calculator website, called aqadvisor.com where you can put in your tank dimensions, the type of filter you have, and what type of fish you want to add. This will calculate what percentage stocked you will be, as well as advise you about water change amounts and frequencies. I have found this calculator to be the most accurate and informative.

**Related Posts:**

**How Many Gouramis Can Fit in a Tank?**

**How Many Loaches Can Fit in a Tank?**

**How Many Cichlids Can Fit in a Tank?**

When it comes to the temperament of Rainbowfish, the vast majority of them are perfect for community tanks as they are a peaceful bunch. A few species can get territorial when spawning, but that’s about it.

**How Many Rainbowfish Can Fit in a 40, 60, 75 or 125 Gallon Tank?**

You may, or may not be aware, that Rainbowfish come in many different shapes and sizes.

For the purpose of the table I have compiled, I have taken 3 different sized species of Rainbowfish. The three that I have chosen are all wide bodied species, which I have taken into consideration:

**The** **Peacock Rainbowfish,** adult size 2.5 inches approx. Other examples of Rainbowfish that grow to around this size are:

Australian Blue-eye Rainbowfish, Forktailed Blue Eye and Dwarf Rainbowfish.

**Boseman’s Rainbowfish**, adult size 4.5 inches approx. Other examples of Rainbowfish that grow to around this size are:

Lake Kutubu Rainbowfish, Bleher’s Rainbowfish.

**Splendid Rainbowfish**, adult size 6 inches approx. Other examples of Rainbowfish that grow to this sort of size are:

Parkinson’s Rainbowfish, New Guinea Rainbowfish.

For the purpose of international peacekeeping, and to make things easier for you, I have compiled information for both gallons and litres.

One thing to consider with Rainbowfish is that they are shoaling fish. They are best being kept in groups of at least 5. Some of the size tanks below aren’t big enough to have a group of them. As said previously, this chart is just to give you an idea of how many fish of that size can be safely housed if suited.

I would use these tables as a rule of thumb. I would always suggest you double check with aqadvisor.com to be doubly certain.

**Rainbowfish Calculator in Gallons.**

**How Many Rainbowfish Will Fit in a 60, 80, 100 or 140 Litre Tank?**

**Rainbowfish Calculator in Litres**

Litre | Minus 10% | Peacock (2.5 inch) | Boseman’s (4.5 inch) | Splendid (6 inch) |
---|---|---|---|---|

25 | 22 | 2 | 1 | 0 |

60 | 54 | 4 | 2 | 1 |

70 | 63 | 4 | 2 | 2 |

80 | 72 | 5 | 3 | 2 |

100 | 90 | 6 | 4 | 3 |

140 | 126 | 8 | 5 | 4 |