How Many Guppies to Keep in a 10 Gallon Tank?

Are you planning to buy a couple of guppies, an aquarium, and mash the two together? That’s a nice idea but how many guppies fit in a 10-gallon tank? Well, this is a question many people are asking themselves. Being the fish-lover that I am, let me enlighten you.

In this article, I’ll give you exact numbers and ways to calculate the number of guppies that you can keep in a 10-gallon tank.

Being a beginner fish owner is no excuse to be uninformed. Without an adequate knowledge base, you may end up overcrowding your guppies, which stresses them out. And stress is the silent killer of all guppy fish, as I’ve described in previous articles. Undercrowding is not really a problem but a precaution. Still, guppies are sociable fish that thrive in a social environment.

How Do You Calculate How Many Guppies Fit into a Tank?

It’s easier than you might expect. No need to undergo extensive math studies at Harvard or whatnot. Use the 1-inch-of-fish-per-gallon-of-water equation, as I like to call it. So, in case it’s still not clear, for every inch of fish, you need a gallon of water. So, if a fish has 2 inches, then you’ll need 2 gallons of water to house it. And the list can go on with 3-inch fish and 3 gallons of water.

One important thing to remember is that you can never fill an aquarium with water to its full capacity. Let’s take a 20-gallon aquarium, for instance. What does it contain, besides water? Well, the substrate, which is about 4-6 inches thick, a couple of decorative plants, a sponge filter, a heater, and so on. These take up space in the aquarium, space that water can’t occupy.

So, a 20-gallon aquarium may only hold up 16-17 gallons of water, depending on how much space other things occupy. I recommend considering this when estimating the number of guppies that fit into a tank. Going by the regular gallons-of-water-per-aquarium-capacity equation would result in overcrowding. The illusion puts your guppies at risk of stress, which we know is a death sentence for fish.

Let’s make a few bullet points for the sake of clarity:

  • An adult guppy generally reaches up to 1.5 inches of body length, without its tail fins
  • In a 20-gallon aquarium, you can put approximately 13 guppies (20 / 1.5 inches = 13.3 fish)
  • With a 10-gallon tank, approximately 7-8 guppies are just right. Don’t go above 10 because then, you’ll be overcrowding them

Is There a Way to Add More Guppies to The Tank?

Let’s be honest there, who doesn’t love an aquarium teeming with fish? You gotta love those colorful dashes happily swimming about, making your day better. A tank without fish is like steak without barbecue sauce, Bonnie without Clyde, Sherlock without Watson, and so on.

Well, there’s good news – you can get around the 1-inch-of-fish-per-gallon-of-water equation, a bit. Rules are meant to be broken, right? Well, you can fracture this rule a bit but not break it completely. Here are a couple of things you can do in this case:

  • Add live plants to your tank, especially fast-growing plants
  • Perform weekly water changes (about 30-50% of the water)
  • Feed your fish only once every other day
  • Buy a good internal or external filter
  • Use a special substrate for guppies (avoid gravel)
  • Get a premium bio filter media like Ehiem Substrat Pro or Seachem Matrix

And because I’m a nice guy, I’ll also explain each element, in particular, starting with…

Live Plants

Every aquarium could do with some plants. We love them, the fish love them, everybody loves them. They look good and add a subtle hint of higher aestheticism to your aquarium. It looks more alive than ever, after putting a few aquatic plants in, right? Not only this but, get this, plants will improve the overall quality of the water by eliminating the toxins from fish waste.

I recommend choosing fast-growing plants because you have no time to waste. The aquarium isn’t going to populate itself, and you need it now. Aquatic plants will also extract plenty of nutrients from the water column, helping the fish stay healthy. As for particular plant species to choose, here’s a handy list:

  • Hornworts
  • Watersprite
  • Amazon sword
  • Guppy grass
  • Java ferns
  • American waterweed (Elodea)
  • Wisteria
  • Amazon frogbit
  • Duckweed
  • Giant duckweed
  • Water lettuce

Perfect, now you’re on your way to increasing the number of guppies in your aquarium. One more thing about plants, though – they need light to grow and survive. So, keep the lights on for at least 6-8 hours every day. Without light, plants wither off and eventually die. They’ll pollute the tank while doing so, as well. So, try providing enough light for them, eh?

Aquarium plant fertilizer is a bonus touch that further helps your plants grow and remain healthy.

Water Changes and Proper Tank Maintenance

The more fish in an aquarium, the more often you’ll need to clean it. Fish waste becomes a real problem with 20+ guppies in an aquarium. If you have a good filter media, you’ll only need to perform weekly water changes (30-50%) but that may not be enough. I recommend paying attention to the tank and watching for pollution. Does the water become muddied sooner than a week? Then a water change is in order.

Clean the aquarium filter media once per week, as well. Don’t think that the filter can’t get filthy because, oh boy, it can. I could tell you about a few particular experiences with dirty filter media that messed up my aquarium. Suffice to say that the fish didn’t escape unscathed from that experience. When washing the filter media, don’t even think about using tap water. The chlorine in it will kill the beneficial bacteria that convert harmful compounds into good ones. You need these bacteria to keep the fish healthy and happy.

Feed Guppies Less Often

Guppies are starved pretty much all the time and they could eat constantly. They’re omnivores, which further adds to their appetite. Whatever they can fit into their mouths, they will eat. But overfeeding is the number one killer of guppies, aside from bad water quality. Overfed fish are more likely to develop diseases and complications like dropsy, stress, and Ick.

But, despite their constant hunger, adult guppies don’t need that much food. In fact, guppies can survive without food for weeks without major problems. From my experience, feeding guppies every other day is an optimal schedule because it keeps them healthy. It’ll also prevent pollution to the water, allowing you to change it less often.

The way I do it is simple. When I want to feed my guppies, I take just a pinch of food and drop it into the aquarium. I won’t give them any more food until they eat everything. Then, I’ll give them food until I estimate they’ve had enough. Flake veggies, pellets, all are ideal for guppies. Just a few pinches and you’re done, though you need to consider the number of guppies you’re feeding, as well.

Internal And External Filter

Usually, when buying an aquarium kit, you’ll also get an internal filter. However, the filter is only good for a decently crowded 10-gallon tank. It won’t work as efficiently on an overcrowded one. So, I recommend buying a bigger filter if you’re planning on putting more than 10 guppies in your aquarium. Bigger filters have better performance, a higher flow rate, and more. In other words, they can take care of more fish at once.

At the same time, I recommend buying an external filter canister to improve the water volume in the tank. Since the external filter won’t take up any place inside the tank, it’s a seamless way of increasing the water level. You can get the Aqueon QuiteFlow 20 HOB filter, for instance. This is a hang-on-back filter that works well on aquariums of up to 20 gallons.

An overstocked 10-gallon aquarium doesn’t exceed its capabilities. Its flow rate is 125 GPH (about 470L/hr), which is clearly enough for your needs. A good canister filter for an overstocked aquarium is the SunSun HW-603B. It has a consumption rate of only 6W and it flows with a power of 100 GPH (400L/hr). All in all, it’s a quiet, efficient, and performant canister filter that’ll keep your guppies healthy.

Filter Media

In regular aquariums, sponge filter media is just enough to filter out all impurities. But an overstocked 10-gallon aquarium is a different beast. It needs something bigger, better, more performant. You’ll need a biological filter that offers enough surface area for the beneficial bacteria to do their thing. Decomposing the harmful compounds like nitrites and ammonia, of course.

I recommend the Seachem Matrix and the Eheim Substrat Pro. The latter is a superb biological filter that offers increased efficiency in dealing with noxious toxins in the aquarium. It’s a bit more expensive than other similar products but that’s what you get for overstocking your aquarium. Take it or leave it! Indeed, cheaper filter media may cover your bases just right, so inform yourself beforehand.

Special Substrate

What’s the most common type of guppy substrate used in aquariums? Gravel, of course. But besides taking up unnecessary space, does it do anything else? Nope, it doesn’t even help the aquarium during the self-cleaning process. So, it’s a good idea to replace the gravel substrate with something like Seachem Flourite. This substrate will produce nitrifying bacteria that eliminate fish waste.

It’s a special type of substrate that costs more than gravel. But it’s a much better choice for an overstocked aquarium. That is, if you want the fish to survive and lead a good life. If you still want to keep the gravel substrate, make sure you vacuum it on every water change. An aquarium gravel vacuum will help you do that efficiently, so make sure you get one.

Wrap Up

While it’s not exactly a good idea to overstock your aquarium with guppies, sometimes you can’t help it. Lively aquariums are irresistible, honestly now. Even I use a combination of substrate, good filters, and aquatic plants to house more guppies in my aquarium. It’s not impossible if you know what to do. And you do now!

Let’s see what you’ve learned in this article:

  • It’s optimal to provide 1 gallon of water per 1 inch of fish
  • Aquatic plants improve the quality of the water, enabling you to house more guppies
  • Better internal and external filters further increase the overall health of numerous guppies
  • A special substrate helps the aquarium self-clean itself
  • Performant filter media gives your aquarium that extra boost in anti-toxin protection
  • Changing the water more often is a necessity with more fish in the aquarium
  • Feeding the guppies less often maintains their optimal health

Good luck with your guppies!

avatar Noah
I’m Noah, chief editor at VIVO Pets and the proud owner of a playful, energetic husky (Max). I’ve been a volunteer at Rex Animal Rescue for over 2 years. I love learning and writing about different animals that can be kept as pets. read more...

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