How Many Guppies in a 20 Gallon Tank?

So you have a 20-gallon tank and are considering getting guppies. These small, colorful fish are great additions to your home. It’s peaceful to look at them swim around. Guppies are generally peaceful and don’t have a “hot” temperament, and they are easy to maintain.  

That being said, you still need to make sure they have everything that’s necessary for a healthy, guppy life. Most people repeat a similar mistake where they put too many guppies into a fish tank just because they’re small, so they believe the size shouldn’t matter. But it does! In this post, you’ll find out how many guppies should be in a 20-gallon tank and learn more about factors that influence their number in an aquarium. 

How Many Guppies in a 20 Gallon Tank? 

Even though you probably expect one specific answer to the “how many guppies in a 20-gallon tank” question, it’s not that easy. You see, the number of guppies in an aquarium depends on various factors. Generally speaking, you can keep 10 to 12 guppies in a 20-gallon fish tank.  

How Do You Calculate How Many Guppies You Can Keep in a 20 Gallon Tank? 

Do not let their petite size fool you; it’s a mistake to add as many guppies as you want into a fish tank. You need to bear in mind guppies need to have a lot of room to swim, and adding too many fish can cause various problems, which will be discussed below.

Yet another thing to keep in mind is that no tank is going to be full from top to bottom due to other pieces of equipment. Therefore, you need to be careful when deciding on how many guppies to add to the aquarium. 

The general formula to calculate how many guppies to add to a tank is one gallon of water per one inch of guppy. In other words, a two-inch guppy needs two gallons of water. Going by this calculation, we reach the conclusion that the ideal number of guppies per 20-gallon tank is around 10, depending on size.

Although it’s entirely possible to keep 12 guppies in a fish tank, it’s not recommended for inexperienced people. If you haven’t had fish, especially guppies, before, it’s not a good idea to start with a high number. Start small and work your way up. 

Now that we have established the ideal number of guppies in a 20-gallon tank, we need to address other important things. Based on this calculation, you could hold 10 (or up to 12, if you’re experienced) females since they can grow 2 inches in size. As far as males are concerned, you could hold 12 to 13 of them in a 20-gallon fish tank. 

If you are to mix things up and hold both genders, then you need to keep their size in mind. You may want to go with one male to two females. So, your fish tank could have three males and seven females, or four males and eight female guppies.  

The priority is to ensure your guppies have a comfortable living environment, oxygenated water, and suitable temperature. The number of guppies in the fish tank isn’t the only thing that matters, but the remainder of the equipment and how well you take care of them. 

Does Gender Matter? 

To inexperienced people, all guppies (and other fish) look the same, and there are no visible differences between males and females. Not true, though! Male and female guppies have a lot of differences, and gender is crucial when calculating how many to hold in a tank.  

Before we discuss the relation of the gender of guppies to tank size, we need to address some differences between males and females. Generally speaking, males have longer and slender bodies, but female guppies look rounder and curvier. That said, females tend to be bigger than males. The male guppies are up to 1.5 inches long, while females can reach two or even 2.5 inches in size. 

Although we would expect a female to be colorful in guppies, that role belongs to a male. Yes, males appear to be more colorful, especially in the tail area, and the best thing about them is that their colors can be quite vibrant and vivid. 

Since males and females differ in size, the calculation of how many guppies should be in a 20-gallon tank may vary, as demonstrated above. Therefore, if you plan to have both males and females, you need to bear in mind that the number of guppies in the aquarium won’t be the same as with a single-gender. In other words, the number of these fish in a certain tank depends mainly on the gender of guppies you choose.  

What Will Happen If You Add Too Many Guppies? 

Due to their small size, it’s easy to think nothing will happen if you add as many guppies as you want into a fish tank. The overcrowded aquarium is not a good idea, which is why you should stick to the calculation mentioned earlier in this post. Adding too many guppies into a fish tank can pave the way to a wide range of problems such as: 

  • Too much ammonia – fish produce ammonia, which can be toxic for them. Despite the fact that every fish tank has a filter that takes care of ammonia, too many fish can still be harmful. Every filter has its limit, so when the tank is overcrowded, it may not work properly to filter the water. When water isn’t filtered, oxygenated, and clean, then fish can’t remain healthy.  
  • Weaker immune system – too many guppies decrease the quality of water due to increased waste. This leads to the cycle, which includes ammonia, nitrite, and nitrate. The filter can’t do much when the fish tank is overcrowded. This leads to a weakened immune system of guppies, i.e., they become more susceptible to disease. In turn, their lifespan also shortens.  
  • Increased stress – when you decide to have a fish tank, the goal is to recreate the natural environment of certain fish, in this case, guppies. These are freshwater fish, and they’re used to swimming in the current. Water in the fish tank shouldn’t be stagnant. Guppies need water movement and a decent amount of space so they can swim freely. The overcrowded aquarium doesn’t allow that. When fish don’t have enough room to swim, they become stressed out. Stress also increases the risk of diseases since it weakens their immune system. 
  • Aggressiveness – with the increased stress of guppies in the overcrowded fish tank, there may also come aggressiveness. Guppies may feel frustrated by all the competitors in the aquarium with them. (Find out more about guppy fighting and aggression.)
  • Developmental issues – guppies aren’t big in size, but too many fish in the tank may impair the growth of young fish. Developmental problems directly harm their quality of life and may shorten their lifespan.  

What Effect Will Breeding Have? 

Guppies breed like crazy, and this is an important factor to bear in mind when deciding how many fish to keep in the tank. The reality is that if you have a male and female guppy in a fish tank, they’ll breed regardless of whether you want that or not. Female guppies can have multiple pregnancies from only one fertilization over a certain period. This can lead to the overcrowded fish tank, which was discussed above. 

Therefore, when deciding how many guppies should be in a 20-gallon fish tank, you also need to take into consideration their gender and the fact they breed a lot. The fish tank has to accommodate your guppies perfectly, so if you’re not ready for them to breed all the time, then you may want to opt for males or females only. If you decide to mix them up and want to prevent excessive breeding, you may want to add more males than females into the aquarium. 

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The number of guppies in a fish tank is crucial. You need to take into account their size and gender when deciding on how many guppies should be in a 20-gallon tank. Males and females come in different sizes, so the same rule can’t apply to both. For example, you can fit more males than females into a tank, but most people prefer to mix them up.  

When adding both genders, always bear in mind these fish breed a lot, so you need to be careful if you want to prevent the overcrowding problem. It’s also important to emphasize that proper care is crucial. Guppies need a warm temperature of the water and hate stagnant water in the fish tank, so make sure to recreate their natural environment the best way you can. 

(Find out how many guppies can stay in a 5-gallon and 10-gallon tank.)

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