There are many different types of freshwater aquariums to choose from. If you haven’t done so already you might want to familiarize yourself with fish compatibility in general as well as with freshwater fish compatibility.
⇐Fish Compatibility and Selection Freshwater Fish Compatibility⇒
Passive Freshwater Community Tank
A freshwater community tank is a type of freshwater aquarium populated by fish that would be considered passive and non-territorial in general. The fish can be schooling or non-schooling or a mixture of the two. In the freshwater aquarium there are many dozens of different species to choose from commonly and widely available. Tetras, Danios, Rasboras, and Hatchets, Cory cats, Dwarf Gouramis, Rainbowfish, Angelfish, Discus, Silver Dollars, and more can all be housed together. Some of these species are bottom dwellers, some prefer to hide in rockwork, some are mid level or upper level fish, and they typically range from very small to fairly large (up to 8 inches for discus.) This is our favorite type of aquarium as many different species and types of fish with a wide range of coloration and patterns can create an endless number of great visual effects in the home aquarium. Also, when done properly there will be very little aggression and will be peaceful and relaxing to observe.
Freshwater Planted Aquarium
A planted aquarium will most commonly be used in conjunction with passive community fish but this is not necessarily the case. You could have more semi-aggressive fish such as Barbs, Freshwater sharks, and Plecos that are still considered compatible with this type of freshwater aquarium. With some caution and planning you can even have plants in a tank with fish such as cichlids and goldfish. A lot of fish such as cichlids and goldfish are not generally considered compatible with live plants because they like to dig at roots but often if you get hardier, more thick leafed plants and cover their roots with rocks so that they will remain undisturbed then it is a challenge but it is possible. For African cichlids you have to find plants that can tolerate high alkalinity. Generally speaking, however, thick leafed Anubias species and Java Fern will work with even a hard water cichlid set up. For more on Freshwater Planted Aquariums see the Aquarium Plants page.
Semi Aggressive Community Tank
Maybe you want a bit more action in your aquarium and a little bit more of a challenge. Aggressiveness is somewhat relative among fish. When a fish is labeled semi-aggressive it usually means, under the right circumstances, the fish can be very aggressive. Very aggressive means it could attack other fish and kill them, eat other fish as food, or relentlessly chase other fish around until they die of stress. These fish will tend to be a little bigger and so need a bigger aquarium … probably 75 gallon at a minimum or larger range.
On the other hand, under the right circumstances, a semi-aggressive fish can be very docile. While we can never know exactly what a fish is going to do in this type of freshwater aquarium, we can predict with a fair amount of success how they’ll react in different situations due to their temperament and natural habits. This means, if we stock our tanks wisely, even a group of semi-aggressive species can live together in relative peace. Typically, these types of tanks do better if the fish grow up together. When mature it can be a challenge to introduce new fish. If you do try to introduce new fish to a mature semi-aggressive tank you will need the new fish to be at least at large as the fish in the tank already, you should introduce several at a time and not singly, and you might even need to leave the lights out for a few days to help get everyone accustomed to one another.
Generally speaking, semi-aggressive fish will do better with fish about the same size as them or bigger. They will also do better if you stock just a single male or make sure you have a higher female to male ratio. This can be a challenge because when young the sex of the fish is much less obvious for most fish. You might have to be prepared to sacrifice a few males as they get older. As they mature the males will be larger and more aggressive than the females and will typically fight with the other males more. If you eliminate the alpha males being really aggressive generally things will calm down quite a lot. Males of different species but that have similar feeding patterns and body types might also fight with one another. An aggressive bottom feeder will probably be compatible with an aggressive mid level fish. If you understand these fish before you stock them, you will have a better chance that everybody gets along, and reduce the chances of too much aggression in your aquarium.
Some fish that might be candidates for a semi-aggressive community tank are cichlids (usually kept in species specific tanks but don’t have to be), goldfish (also usually kept in species specific tanks but don’t have to be), barbs, plecos, freshwater “sharks”, larger Gouramis, larger catfish, Loaches, and more. Scats, fish in the genus Monodactylus or “Mono’s”, Dragon Gobies, Figure 8 puffers, and Columbian Sharks are good for a Brackish water Semi-aggressive tank.
A Betta tank is the most simple type of freshwater aquarium a person can have. They typically do well in small 1-2 gallon tanks and just need a little water movement and aeration and an occasional water change. Betta males are of course beautiful fish but fiercely aggressive and will fight another male to the death … even with no female to watch! They are hardy and typically intended to be kept as solitary fish. Could they even be kept with other fish??? We don’t know but doubt it.
Goldfish are very frequently kept in a species specific type of freshwater aquarium. This is because they like water that is much colder than most other fish commonly sold in stores, between 65-75 degrees Fahrenheit. The tanks are normally fairly sparse with some gravel and maybe a few rocks and decorations. If you keep the tank around 74 degrees then a pleco or most catfish will do just fine as a bottom feeder tank mate. It is possible to keep some types of other fish such as sharks or gouramis in a goldfish tank but you really have to pay attention to the temperature requirements. For example, discus like their water to be much warmer and could not be kept with Goldfish. Gouramis and sharks will do ok at 72-74 degrees but it shouldn’t get much colder than that. Any plants really need to be tough and tied down with their roots hidden. See the Aquarium Plants page for more information on keeping plants with goldfish.
Cichlids, especially African Cichlids, are another type of fish that are often kept in a species specific type of freshwater aquarium. This is because African Cichlids like very hard water with a pH of around 8.2, much higher than almost all of the other freshwater fish commonly available. Most African Cichlid tanks will have a pleco or similar large heavy duty catfish as a bottom feeder. Even though plecos like softer water they will normally adapt, especially if you keep the pH around 7.8-8.0 which is at the low range of the pH African Cichlids should be kept at. So why keep African Cichlids? There are literally over a thousand species and are among the most colorful of any freshwater fish and you can get a combination of bright solid yellow, blue, white fish as well as many different striped and other color variations. They are very hardy and although very aggressive, typically will do well with each other and can be stocked at fairly high densities. They will do even better if you eliminate some of the more aggressive males as they mature or you can just let them duke it out and enjoy the fights.
South American Cichlids are very similar but like neutral water with a pH of around 7.0 and can be successfully kept with a far greater variety of other fish. Oscars are extremely large South American Cichlids and are often kept in species specific tanks due to their sheer size.
Cichlids like a rocky aquarium with lots of holes in the rockwork or “caves” for them to call their own. Live plants in this type of freshwater aquarium are a big challenge but possible, see the Aquarium Plants page for more information on keeping plants with African or Freshwater Cichlids.
Discus are a passive fish and would be great in any community aquarium except for the fact that they really prefer soft and very warm water, 79-86 degrees. This is a lot warmer than even most other South American fish but if you keep it at about 80 degrees and the water right around neutral then they can actually be housed with a wide variety of peaceful tank mates such as tetras, rainbowfish, cory cats, and dwarf gouramis. Live plants are not a problem in a discus tank. Fish like cichlids or goldfish are definitely out in this type of freshwater aquarium however.
Large Oddball Community Aquarium
There are actually quite a lot of large freshwater fish that when housed with other similar sized fish will be quite peaceful and make for basically a really large freshwater community tank. Of course, you will most likely have to buy them small and let them grow up with one another and this will contribute to their peacefulness towards one another when full grown. Of course, in this type of freshwater aquarium, once fully grown any smaller fish thrown in the tank will simply be “food.” This is a great idea but you really need a big tank for this … the bigger the better. I’m talking 300-1000 gallon aquarium system but when it’s done well it can make for a spectacular sight worthy of a museum of theme park. Arowanas, large catfish, Loaches, Bichirs, Bala and Columbian sharks, freshwater eels, Rope fish, and more are some of the freshwater fish that can grow to over 1 foot long in an aquarium AND actually be kept with one another with a neutral pH and a temp of about 78 degrees! I’ve seen a few tanks like this in the 1000 gallon range and if you have the resources and space you can really have a jaw dropping aquarium that with some denitrification can actually be pretty affordable and easy to maintain. I sooo want to do this but alas … my house is just way too small.
Brackish Water Aquarium
It’s not surprising that there are many fish that do well in brackish water as there are many large areas of the world where freshwater meets the ocean. Brackish water has both a relatively high pH, usually around 7.6 is good (a little lower than African Cichlids like) and also prefer some marine salt in the this hybrid type of freshwater aquarium. You don’t need a lot of salt but 1/8 cup up to 1/4 cup of salt per gallon is usually ideal. A Saltwater aquarium has a specific gravity salinity of 1.022-1.026 and a brackish water tank will have a specific gravity salinity between 1.005 to 1.015 on the high side with 1.010 being in the mid range.
You can actually set up a passive community brackish tank, a semi aggressive community brackish water tank, or even stick to just one or two species. Mollies are the Tetras of the brackish water tank and platies and swordtails are related and can be acclimated to brackish water as well. In addition to those fish, figure 8 puffers, Scats, Monos, Columbian Sharks, Bumblebee and other freshwater Gobies, and more will do well in a brackish water aquarium.
Many plants that are available will not do well in brackish water tanks. Java Moss and Java Ferns, Bacorpas, and crypts among others are reportedly able to be acclimated to a brackish tank. Mangroves are an option but they will need to actually grow out of the tank. For more information see the Aquarium Plants page.
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