If you’re looking for the best fish for a small tank without a heater, then you’re in luck because you have a lot of options. In the following article, we’ll review the eight best coldwater fish for small tanks that are readily available on the market.
You might also want to try out our Aquarium Heater Size Calculator (Click Here) to see what size heater you would need for your aquarium.
Best Fish for a Small Tank without a Heater
| Image | Name | Temperature | Rating | Shop |
|---|---|---|---|---|
 | GloFish (Danio) | 64°-75° F |  | |
 | White Cloud Minnow | 64°-72° F | | |
 | Guppy | 64°-82° F |  |
GloFish (Danio)
GloFish (Buy Online) are a unique freshwater fish that can tolerate a wide range of water conditions. Their hardy nature makes them the perfect first fish for children and beginners. And their bright vibrant colors can even rival the colors of fish found in saltwater aquariums.
GloFish can handle water temperatures that range from 64-75 degrees Fahrenheit. As long as you can keep them within this temperature range they won’t need supplemental heating. One caveat is that GloFish will be more active if the temperature is above 72 degrees Fahrenheit.
GloFish 5 Gallon Crescent Aquarium Kit
GloFish are perfect for small tanks since they are a relatively small fish that only reach a maximum size of about 2.5 inches. If you try to follow the recommended stocking density of one inch of fish per one gallon of water. You will easily be able to keep a small school of up to five GloFish in a 10-gallon aquarium.
White Cloud Minnow
The White Cloud Minnow (Buy Online) is a small fish that is very tolerant of cold water. They are also very easy to care for since they are not picky about water conditions. And they will brighten up a tank with their golden bodies and vibrant red markings.
The white cloud minnow is very well adapted to living in cool water conditions. This stems from the fact that they are native to the Chinese Cloud Mountains. At those high altitudes, temperatures remain cold for most of the year. White cloud minnows are able to comfortably live in temperatures ranging from 64-72 degrees Fahrenheit. And they will breed and remain active, even when they are kept at the low end of that temperature range.
White Cloud Minnows will be much more active if they are kept in schools of at least five or more fish. And their color will even brighten up when they are around each other. And white cloud mountain fish are a small fish that don’t grow much larger than 2 inches. So even if you have a small tank, you will be able to keep a school of these very social minnows.
Guppies
Guppies (Buy Online) are one of the most well known colorful freshwater fish. They are usually the first fish people get when they are just starting out in the fish keeping hobby. And that is for good reason since they are a very versatile fish that can survive in a wide range of conditions.
Even though guppies are a tropical fish they can handle water temperatures that range from 64-82 degrees Fahrenheit. This wide range of acceptable temperatures means you can easily keep a guppy in an unheated aquarium. Just be aware that if you want to breed your guppies, they will only breed when the water temperature is above 77 degrees Fahrenheit. And as with most tropical fish, they will be more active and playful at higher water temperatures.
Keeping guppies in a small tank should not be a problem. Guppies are a small freshwater fish that reach a maximum size of 2.5 inches. If you have a small tank you should be able to keep a few guppies without running into any problems. As usual, just try to follow the rule that one inch of fish requires one gallon of water. If you stick to that rule it will prevent you from having any of the problems associated with overstocking an aquarium.
Platies
Platies (Buy Online) are easy to care for fish that add color and activity to any aquarium. These attributes make platties a great first fish for beginners. They also give birth to live young, so they are the perfect fish to introduce someone to the fun of fish breeding.
Keeping platies in an unheated tank won’t be a problem since platies can handle water temperatures that range from 64-77 degrees Fahrenheit. As long as the temperature in your tank remains relatively stable and doesn’t swing wildly then platties will do just fine. But if you do want to breed your platties they will need to be kept in water that is above 77 degrees Fahrenheit.
Platies are small fish that don’t grow much larger than 2 inches. Platies are also more tolerant of cramped conditions then similarly sized guppies. And in a worst-case scenario, they can handle being in an overstocked tank since they are very tolerant of poor water conditions. You should of course always stock your small tank appropriately, and try to avoid having any more than one inch of fish per gallon.
Endler’s Livebearer
Endler’s Livebearer is an extremely hardy small freshwater fish that not many people are aware of. Endler males are beautiful fish that exhibit hues of orange, green and blue all across their body. They are so colorful they even make a great substitute for neon tetras, especially in a cold water aquarium.
Endler’s are native to northern Venezuela where they live in shallow streams and lagoons. These shallow bodies of water can experience wide swings in temperature and water quality. Because Endler’s evolved in those conditions, they can live in water temperatures that range from 64-82 degrees Fahrenheit. And they will breed and remain active even when they are kept at the low end of that temperature range.
Endler’s are a very small fish that only reach a maximum adult size of 1 inch. Their small size makes them a perfect fish for a small tank. They do like to swim around a lot so they will appreciate a large tank if you can provide them with one. But if all you have is a five or ten-gallon tank you will still be able to have a nice school of Endler’s.
American Flagfish
The American Flagfish is a very easy to care for Killifish that can thrive in very small tanks. Since the American Flagfish is a Killifish they are able to breath atmospheric oxygen. That allows them to live in very cramped conditions just like Bettas.
The American Flagfish is native to Florida where they live in shallow swamps and marshes. And for short times they can even live on land if they have to. This wide range of adaptability allows them to survive in temperatures that range from 66-72 degrees Fahrenheit. But they are more active when the water temperature is at least 70 degrees Fahrenheit.
Since American Flagfish live in swamps, they are used to living in small bodies of water. Sometimes they even have to live in a puddle for short periods of time since swamps can experience rapid water level changes. And they only reach a maximum adult size of 2.5 inches. And to top it all off they can survive in water that has a very low concentration of dissolved oxygen. When you put all of these things together you get a fish perfectly adapted to life in a small aquarium.
Mosquito Fish
The Mosquito Fish is a small fish that comes from the same family as guppies. And because of this relation, they have the same ability to adapt to different water conditions. And as their name implies they are voracious consumers of mosquito larva.
Mosquito fish can live in water temperatures that range from 65-75 degrees Fahrenheit. And they are very tolerant of poor water conditions. Due to their ability to handle poor water conditions they are even added to stagnant backyard pools to help control mosquito populations.
Mosquito fish are not the smallest fish on this list, so you might not be able to keep as many in a small aquarium. An adult mosquito fish can reach a size of up to 3 inches. That might mean you will only be able to keep a few of them in a small tank. Or you can keep a small school if you have a tank that is close to twenty gallons.
Comet Goldfish
Comet Goldfish (Buy Online) are the smallest and easiest to care for of all the goldfish. And you may have even seen these fish being given away at a local carnival as a prize. When most people think of a pet fish the Comet goldfish is usually the first fish that pops into their mind.
Goldfish are one of the most cold water tolerant fish available. They can easily handle temperatures that range from 65-75 degrees Fahrenheit. And some goldfish even survive outside in ponds throughout the winter. They have even evolved to enter into a state of quasi-hibernation to survive such extremely cold temperatures. But in a tank that stays at least above 65 degrees Fahrenheit they will remain active year round without having any problems.
The only downside of keeping a Goldfish in a small tank is that they will eventually outgrow it. At first, they will be small so they will easily fit in a small tank. But eventually, they will grow to a size of up to 12 inches, which is way to big for a small aquarium. If you only plan on keeping a goldfish in a small tank when they are young this won’t be a problem. As they get older though you will have to upgrade their tank since they will eventually outgrow the tank they started in.
![Best Filter for an Oscar Fish Tank Oscar fish are voracious eaters that can grow to be up to 14 inches long. They need a lot of space and a big tank, but they also need good filtration. This is because Oscars produce a large amount of waste for their size, which can quickly pollute the water if not managed properly. Read on to see the best filter for an Oscar fish tank. [toc] Best Filter for an Oscar Fish Tank ***TABLE**** Best Filter for an Oscar Fish Tank OASE Indoor Aquatics Biomaster Thermo 600 The Aquatics Biomaster Thermo 600 Filter (Buy Online) has everything you need to keep water clean and healthy for your fish, plus some cool extra features too. It comes with four different filtration stages that remove debris from the water so your tank stays clear and safe for your fish to live in. Plus, it has a built-in heater which keeps the temperature of your tank consistent so you don't have to worry about fluctuations or sudden changes affecting your fish. The OASE Indoor Aquatics Biomaster Thermo 600 is a reliable and high-quality filter that will keep your water crystal clear. It has four stages of filtration, including a pre-filter module for particle removal, two main filters to clean detritus from the water before it reaches the pump area, an activated carbon stage with 45 ppi pores to trap organic chemicals and reduce odors, and finally a polishing cartridge which traps any particles left after the other three stages have removed most of the large debris. Plus, it comes with Hel-X Biomedia that has an extremely large surface area for beneficial bacteria colonies that break down nitrogenous waste. Overall, this filter can be used on 70 to 160 gallon tanks, and if you want peace of mind about how well your tank is being filtered and heated – this canister filter is perfect for an Oscar tank. Eheim Pro 4+ 600 Filter The Eheim Pro 4+ 600 Filter (Buy Online) is the best filter for an oscar fish tank because it’s easy to use and maintain while providing a high level of filtration. It has a self-priming pump that makes starting up very simple, plus its safety hose adapter means you won’t have to worry about any accidents with this unit. We recommend going with their Pro 4+ model which has been designed specifically for tanks containing Oscars and other larger species of fish. This filter comes with everything you need including extra media baskets, spray bars, adjustable flow control valves, and more. Polar Aurora 4-Stage External Canister Filter 525GPH with 9-watt UV Light The Polar Aurora External Canister Filter (Buy Online) is an affordable yet high-quality canister filter and it has four stages of filtration (biological, mechanical, chemical and UV) that keep your fish tank crystal clear without taking up much space. If you have an Oscar Fish Tank, then you know that they are messy fish. They produce a lot of waste and your tank needs to be cleaned frequently. That's where this filter comes in handy. It can handle tanks up to 200 gallons and has a maximum flow rate of 525GPH from the built in pump. This is more than enough power for even the messiest Oscar Tanks. This unit also comes with three different media trays so you can use any type of filtration media you want - bio balls, sponges or ceramic rings. And not only does this filter provide excellent water filtration, it comes with a built in 9 Watt UV Light that allows it to easily control algae spores/bacteria and maintain clear water in your aquarium at all times. Fluval FX4 High Performance Canister Filter, External Aquarium Filter The Fluval FX4 (Buy Online) is an external filter designed specifically for aquariums housing oscars and other large tropical fish species like cichlids and catfish. There's also three different filtration stages included in this setup which will ensure that all the waste produced by your fish gets filtered out quickly leaving behind crystal clear water every time. The Fluval FX4 is the best aquarium filter on the market because it has a patented self-priming pump that moves 700 US Gal of water per hour. It also comes with all of the media you need to get started filtering your tank immediately after installation - no extra purchases necessary. This external aquarium filter is easy to install, maintain, and clean. With its multi-stage filtration process this canister filter removes harmful toxins from your water while providing superior mechanical filtration through three stages of bio-filtration using BioMax cartridges, activated carbon pads and biological ceramic rings . This powerful filter pumps out 700 US Gal (2650 L) of water per hour so it's perfect for even the largest freshwater or saltwater tanks up to 250 US Gal (900 L) Best Hang On Back Filter for an Oscar Fish Tank AquaClear Fish Tank Filter, Aquarium Filter for 60- to 110-Gallon Aquariums The AquaClear 110 (Buy Online) is a hang-on back filter that has an adjustable flow rate, and it'll last you for years. AquaClear filters make it easy, convenient, and affordable to keep your tank clean without all of the complexity and hassle of a canister filter. The AquaClear 110 filter has been designed with the hobbyist in mind; and it provides superior mechanical, chemical as well as biological filtration media at an unbeatable price point. It's ideal for aquariums up to 110 gallons (416 liters) in size and it has a flow rate of 500 U.S. gallons per hour (1,900 L/h). SeaChem – Large Aquarium Fish Tank Filter, Tidal 110 Gallon The SeaChem Tidal 110 Gallon Aquarium Filter (Buy Online) is one of the few hang on back filters specifically designed for Oscars and other larger tropical fish tanks (up to 110 gallons). This means that it has more than twice the capacity of other hang on back filters so there's no need to clean out debris as often. It also has an adjustable flow control valve - just set the dial where you want it and let the self-priming pump do its job. You can also use any kind of filtration media without worrying about clogging since the patented impeller design keeps everything running smoothly Best Sponge Filter for an Oscar Fish Tank Bacto-Surge Hikari Aquarium Solutions Foam Filter, 125 Gallons Bacto-Surge Foam Filters (Buy Online) are made from a durable foam material which allows them to last much longer than traditional sponge filters. They also don't require any electricity or have any moving parts, so you can use these as a cheap and reliable way to supplement the filtration in your Oscar tank. Best Under Gravel Filter for an Oscar Fish Tank Lee's 125/135 Premium Undergravel Filter, 18-Inch by 72-Inch Lee's 125/135 Premium Undergravel Filter (Buy Online) is the best you can get for an Oscar fish tank. It has a multi-level plate design made of high-quality plastic, so it lasts longer than standard models. And this under gravel filter can also be used to build an anoxic filter to lower nitrates, which improves overall water quality and it will also help keep your fish healthy and disease free. Best Filter Media for an Oscar Fish Tank Premium Authentic Pinky Filter Floss for Fish Tanks Premium Authentic Pinky Filter Floss for Fish Tanks (Buy Online) provides two layers of filtration to keep your tank cleaner & running more efficiently than ever before. It's made in the USA from high-quality materials that are safe for both fish and humans alike. It also reduces maintenance time because it lasts 2x as long as other brands on the market today. AQUANEAT Aquarium Filter Sponge Open Cell Foam Sheet Bio Sponge Filter Media Pad Aquaneat's Black Fine Filter Sponge (Buy Online) is made with natural materials that are non-toxic and safe for fish & plants. It provides mechanical filtration by trapping dirt particles in the pores of the sponge material so they do not get through into your aquarium water where they could cause harm to your aquatic pets. The open cell structure of the Aquaneat Sponge means you can simply rinse it under running water when needed instead of having to replace expensive filters every few weeks. And we've tested these pads with many different types of tanks and they are one of the most durable and economical ways to keep the water in a fish tank free of debris. Seachem Matrix, 4 L / 1 gal. Seachem Matrix (Buy Online) removes ammonia, nitrite and nitrate from the water column in freshwater tanks through a process called denitrification. It does this by providing an environment where beneficial bacteria thrive and convert harmful toxins into less harmful forms (even anoxic bacteria that break down nitrates). This process reduces stress on aquarium inhabitants by reducing their exposure to these toxins while also maintaining pristine water quality in your aquarium Eheim AEH2507051 Mech Filter Media for Aquarium, 1-Liter Eheim Ceramic Cylinders (Buy Online) are reusable so you don't have to waste money on disposable filter cartridges or sponges every time you clean your tank. Simply rinse them out in decholorinated water when they get clogged, and you can reuse them indefinitely. Oscar Fish Tank Size A 70 gallon tank will work for an Oscar, but it's better to keep them in a 100+ gallon tank. The bigger the better. More space promotes greater health while also keeping them happier which in turn reduces the risk of stress and disease. Oscar Fish Water Parameters Oscar Fish Water pH Level Oscars prefer water with a pH between 6 and 8, but they prefer slightly acidic water and they can live in water that has a pH as low as 5.5 quite comfortably. Oscar Fish Nitrite Level The nitrite level in your tank should be at 0 ppm once your tank has cycled. Nevertheless, a weekly 10% water change with fresh water from the tap is always good early on in the cycle to reduce nitrites. Oscar Fish Nitrate Level To keep your Oscar healthy you want to keep your nitrate levels between 10-40 ppm. It's important that you test the water with a Nitrate Test Kit (Buy Online) to ensure the nitrate levels in your tank aren't reaching dangerous levels. If the nitrates in your tank stay consistently over 40ppm, it’s time to clean or replace old filters, clean out uneaten food, vacuum the gravel, and do at least a 25% water change. Oscar Fish Water Temperature The ideal water temperature for Oscars is 75-80 degrees Fahrenheit (23 - 27 Celcius). It's important to remember that Oscar Fish are from the Amazon Rainforest and they need a heater in their tank especially during the winter time If you want to know what size heater you need for your tank you can use our Fish Tank Heater Calculator (Click Here) Oscar Fish Water Change Water changes are an essential part of fish keeping for any type of fish. This is especially true when you have larger fish like oscars that produce more waste. Water changes, or partial water changes, should be done every 1-2 weeks depending on how many fish you keep in your tank Why Is My Oscar Fish Tank Cloudy Fish tank water can become cloudy for a few reasons. The most usual is that the aquarium is either experiencing a bacteria bloom or there is algae in the water column. If this is the case, you’ll need to do a 50%-75% water change immediately. You can also use an inline UV filter if water changes and regular tank maintenance aren't getting control of your cloudy water problem. How To Keep an Oscar Fish Tank Clean Water Changes Vacuum the Gravel Bed Cleaning the Filter Removing uneaten food from tank Check for any algae growth on plants or glass walls of aquarium and clean as needed Test the water regularly Do Oscar Fish Need a Filter Yes, Oscar fish need a filter because they are messy eaters that produce a lot of waste. The filter helps with this issue and also improves the water quality by converting harmful ammonia into less toxic nitrates.](https://thepetsupplyguy.com/wp-content/uploads/Best-Filter-for-Oscar-Fish-Tank-464x290.jpg)
