Tank Size
Fish
How Many Fish per Gallon
The most often quoted “rule” for how many tropical fish per gallon of water is one inch of fish per gallon of water. This advice works well for most slender-bodied fish, but it is not sufficient for larger wide bodied fish. The one inch per gallon rule also only applies to a fishes adult size, and not the size it is when you purchase it as a juvenile.
For fish with a less slender build, you will have to adjust the one inch per gallon rule to account for their larger overall size. A fish with a medium sized body will, for the most part, require 2 gallons of water for every inch of body length. While a large wide-bodied fish will need at least 3 gallons of water for every inch their body measures.
Another thing to take into consideration is the actual amount of water that is in your tank. While a tank might be rated to hold a certain amount of water, that doesn’t mean it will hold that much when fully setup. The gravel, decorations, and equipment will all displace water to a certain extent, which will reduce the overall water volume in the tank by up to ten percent.
Given that your tank will most likely be holding ten percent less water when it is fully set up, it’s best to consider using that amount as your basis for calculating how many fish you can add. For example say you have a 20-gallon tank, in that case, ten percent of 20 gallons is 2 gallons, so you would base your stocking level on 18 gallons instead of the full 20 gallons your tank is rated for.
For the most part, the one inch per gallon rule is a quick and easy way to estimate the amount of fish you can add to your tank, but it does have some problems. If you prefer a more scientifically sound method of determining a tanks stocking level, continue reading on for an explanation of the surface area calculation.
How Many Fish (Surface Area Calculation)
The surface area calculation is 1 inch of fish for every 12 square inches of water surface area. This calculation will also need to be adjusted for wide-bodied fish to 1 inch of fish for every 20 square inches of the waters surface area . The surface area of a tank can be measured simply by finding the length and width of your tank and multiplying those two numbers together. If you have a specialty tank like a hexagon or a cylinder, all you will need is the side length or the diameter, and then enter it into the calculator above and it will solve do all the work for you.
The surface area calculation takes into account the amount of water that is exposed to the air and not just the total amount of water. This method gives a more accurate gauge of how many fish can live in an aquarium since oxygen and carbon dioxide exchange can only happen at the surface of the water.
One of the hard limits on how many fish you can have in a tank is the amount of oxygen in the water. If there is insufficient gas exchange to keep the oxygen level constant your fish will struggle to breathe. That’s why the surface area calculation is used in large commercial fish facilities, and for calculating a ponds carrying capacity.
While there are things you can do to increase gas exchange like adding and air-stone or agitating the surface of the water. It is still wise to limit the amount of fish in your tank to a level that can be sustained by passive oxygen diffusion. This will help protect your fish in the event of an air pump malfunction or a power failure.
How Many Fish Can be in a 5 Gallon Tank
| Slender Fish | Medium Fish | Large Fish |
| 5 in. | 2.5 in. | 1.66 in. |
A 5 gallon tank can hold 5 inches of slender fish quite comfortably. Five gallon tanks are a nice starter tank for a child, or for someone new to the fish keeping hobby. A five gallon tank is well suited for fish that remain small throughout their whole lives like guppies or neon tetras.
While it might be possible to house medium bodied fish in a 5 gallon tank it is not advisable. The amount of waste they will produce can overwhelm such a small volume of water. A medium sized fish will also be very cramped in a 5 gallon tank since they will have very little room to swim around in.
If you want to house the most fish possible in a 5 gallon tank you should consider getting a school of neon tetras. They are very active colorful fish that will swim around all day, and they are very easy to care for making them perfect fish for beginners.
How Many Fish in a 10 Gallon Tank
| Slender Fish | Medium Fish | Large Fish |
| 10 in. | 5 in. | 3.33 in. |
A 10 gallon tank can hold up to 10 inches of slender fish or 5 inches of medium bodied fish. Ten gallon tanks are the perfect tank for holding a small school of GloFish, neon tetras, guppies or platies.
If you plan on getting GloFish you can read our article on how many GloFish will fit in a 10 gallon tank. Or you can mix and match fish like guppies and other slender bodied fish to have some variety.
It is possible to keep a medium bodied fish in a ten gallon tank, but it will be a little crowded. You will be limited to five inches of fish in that case, which means you will only be able to keep one fish. This is mainly due to the fact that most medium bodied fish grow to a length of a least 3 to 4 inches, so you won’t be able to keep more than one without pushing the tank to its limits.
How Many Fish for a 20 Gallon Tank
| Slender Fish | Medium Fish | Large Fish |
| 20 in. | 10 in. | 6.66 in. |
A 20 gallon tank can hold 20 inches of slender fish, 10 inches of medium fish or 6.66 inches of large fish. Since twenty gallon tanks are so popular the question of how many fish can a 20 gallon tank hold comes up a lot. A 20 gallon tank is large enough that you can house medium bodied species of fish or large fish if you really like a challenge.
A 20 gallon tank will easily house fish like rainbow sharks, tiger barbs and gouramis. They can also house some smaller cichlids like convicts, blood parrots, and German blue rams. If you still prefer to house as many fish as possible in a 20 gallon tank, then you can get a small school of slender bodied fish which can really fill a twenty gallon tank out.
While it is possible to house larger bodied fish in a 20 gallon tank it is not advisable. Since most larger bodied fish easily reach a size of 5 to 6 inches they will be right at the limit of the carrying capacity of a 20 gallon tank. A larger bodied fish will also produce more waste which will require more frequent water changes and filter maintenance.
How Many Fish Can a 29 Gallon Tank Hold
| Slender Fish | Medium Fish | Large Fish |
| 29 in. | 14.5 in. | 9.66 in. |
A 29 gallon tank can hold 29 inches of slender fish, 14.5 inches of medium fish or 9.66 inches of large fish. A fish tank that holds 29 gallons of water is just around the point where you can start considering housing larger bodied fish.
Some good fish for a 29 gallon tank are angel fish, South American cichlids or fancy goldfish. You can also mix and match small and medium-sized fish in order to create a more natural look in the tank.
When it comes to large-bodied fish a 29 gallon tank is just at the bare minimum you will need to house them. In most cases, you can keep up to two large-bodied fish in a 29 gallon tank without any problems. You will have to keep and eye on water conditions since 29 gallons is still not a lot of water to work with. There also might be more territorial conflicts in a 29 gallon tank since space is limited.
How Many Fish Can be in a 30 Gallon Tank
| Slender Fish | Medium Fish | Large Fish |
| 30 in. | 15 in. | 10 in. |
A 30 gallon tank can hold 30 inches of slender fish, 15 inches of medium fish or 10 inches of large fish. A thirty gallon tank has just enough room that you can really start to broaden your fish keeping horizons.
Some good fish for a 30 gallon tank are German rams, American flagfish and tiger barbs. A 30 gallon tank will also work well with a mix of small and medium sized fish. Another option is to add only small slender fish, in that case you will have a decent sized school of fish which can be quite impressive when they all swim together.
If you prefer large fish a 30 gallon tank will easily house certain species of large-bodied fish. You will be able to keep 2 large fish as long as the species of fish you plan on keeping stays under 5 inches when it is fully grown. A better option would be to keep a single large aggressive fish that prefers being kept alone. This will work out well for the fish, and it will allow you to keep a fish that you otherwise wouldn’t be able to.
How Many Fish in a 36 Gallon Bowfront
| Slender Fish | Medium Fish | Large Fish |
| 36 in. | 18 in. | 12 in. |
A 36 gallon bowfront can hold 36 inches of slender fish, 18 inches of medium sized fish or 12 inches of large fish. A thirty six gallon bowfront is not only a very attractive aquarium it also holds a decent amount of water. A 36 gallon fish tank has more than enough space to house most medium and large-bodied fish species.
Some good fish for a 36 gallon bowfront are African cichlids, South American cichlids and large fancy goldfish. A bowfront aquarium will also be even more impressive when it is fully stocked with live plants, so you also might want to consider adding shrimp and snails and other algae eaters to help with tank maintenance.
A 36 gallon bowfront will house a total of 12 inches of large-bodied fish quite easily. If you choose a species of fish that remains under 6 inches you will have just enough room to keep two fish. You could also keep a single fish that will grow to about 10 to 12 inches if you prefer going the route of keeping a single fish as a focal specimen.
How Many Fish Can be in a 55 Gallon Tank
| Slender Fish | Medium Fish | Large Fish |
| 55 in. | 27.5 in. | 18.3 in. |
A 55 gallon tank can hold 55 inches of slender fish, 27.5 inches of medium sized fish or 18.3 inches of large bodied fish. Fifty five gallon tanks are one of the most popular large tanks in the fish keeping hobby. And that is for good reason since they have enough room to keep any size fish you like without taking up a lot floor space.
Some good fish for a 55 gallon tank are Discus, Jack Dempsey and Blood Parrots. A 55 gallon tank can also be used to house a large school of small fish, or you can add a mix of small and medium sized fish so you can have fish at every level of the water column.
Large fish do especially well in a 55 gallon tank, and in most cases it is the minimum recommended tank size for most large fish species. If you select a large species of fish that only grows to 6 inches in length then you will be able to house three of them quite comfortably. And if you really want to push it you can keep two 9 inch fish in a 55 gallon tank, which is perfect if you want to set it up as a breeder tank.
![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)
