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How to Care for Freshwater Tropical Fish

Updated on April 11, 2012
Photo copyright Ales Tosovsky via Wikimedia Commons
Photo copyright Ales Tosovsky via Wikimedia Commons

The most popular and easy to keep category of fish are the freshwater fish. Because of the significantly lower amount of equipment needed to keep these fish healthy, freshwater fish are also much less expensive to keep. The internet is full of all sorts of helpful information on how to keep tropical fish. Unfortunately, it’s very difficult to tell which information useful or not since so much is written by people who are also relatively new to the hobby and have limited experience with different types of fish. After 15 years of breeding and keeping all manner of tropical fish, the basics of care are very obvious and not nearly as difficult as beginners seem to think. Most types of fish sold in pet stores are very hardy and can survive with even the most rudimentary knowledge of their needs.


The first thing to decide is whether you want to choose fish to fit your tank, or a tank to fit your fish. If you have specific fish in mind and have done all the research on them, then select a tank that’s at least 20% larger than the suggestions. Why the difference in size? While 20% may not give you much wiggle room (thus more is generally better) it will give you some space if a fish gets larger than expected, they have surviving fry, or you decide to add a few tank mates on which you hadn’t planned.

Alternatively, you can opt to select fish to fit the tank. In this case, you can choose a tank that fits your budget or fits perfectly into that space you have waiting at home. This is by far the easiest option, as it allows for research and careful selection of all the fish available after purchase. You will have a couple of weeks to make these decisions after you buy the aquarium before it will be ready for fish unless you have media from an established tank to seed in.


All fish need a filter. Without a filter, that fish is swimming around in its own waste and uneaten food and it will be nearly impossible to keep the aquarium healthy. Not all fish need an aerator. Labyrinth fish such as bettas and gouramis breathe from the surface of the water and do not have to rely on dissolved oxygen in the water. Additionally, there are a couple of types of filters that remove the need for aeration by providing surface agitation which will facilitate the oxygen exchange necessary for aquatic life. Without proper oxygen exchange, you have a stagnant pool of water that will be unable to support much, if any, life.

There are differing views on the best type of filter, but the best bet is always to do your own research. Generally the choice in stores is limited to either a HOB (Hang on Back) filter or an undergravel. Undergravel filters are, almost always, a complete waste of money. These filters have insufficient mechanical removal and a very small surface for biological filtration, in addition to clogging easily and making gravel vacuuming more difficult. HOB filters, on the other hand, have effective mechanical and biological filtration and provide a surface current for healthy oxygen exchange. However, HOB filters can be dangerous to weaker swimmers and fry, so many breeders opt for a sponge filter or two for those fish.

The filters sold in stores are rated according to the minimum filtration requirements for small-medium freshwater tropical fish that are primarily herbivores. In other words, unless you have a perfectly-stocked or understocked community tank, that suggestion isn’t going to work for you. Instead, look at the information on each filter for the number of gallons per hour (GPH) it turns over. For small-medium community fish, you’ll want no less than a 4x turnover per hour (i.e. 80GPH for a 20G aquarium). Larger freshwater community fish require no less than a 6x turnover, and goldfish, large carnivores, and most amphibians require a 10x turnover.


This is the most important step in setting up your aquarium. Fish can live without a substrate, they can live without decorations, and they can live without fancy lighting. Fish can not live in an improperly cycled tank. Uneaten food and fish waste produce ammonia. Even in extremely low concentrations, less than one part per million, ammonia will kill very quickly. Through the cycling process, you’re giving beneficial bacteria a chance to establish colonies in the aquarium. This bacteria will break down the ammonia into less-toxic nitrite, which will then in turn be broken down into far less toxic nitrate. Nitrates must be removed mechanically, which will be discussed under cleaning. Some people jump-start the process with some liquid ammonia that doesn’t have any soap or other additives, while seeding filter media or gravel from an established tank may jump past most of the cycling process. Water from an established aquarium likely won’t work as there are very low levels of bacteria in the water, most fasten themselves to underwater surfaces.

There are several methods for cycling, though the days of using “throwaway fish” for cycling are over as the process is extremely inhumane and unnecessary. The easiest method of cycling is to set up your entire aquarium with water, filtration, and heater functioning. Tap water will need to be treated with a good dechlorinator such as Jungle Start Right; you’ll want a dechlorinator that neutralizes chlorine, chloramines, and potentially harmful metals. Bottled water is not recommended for fish because it has no minerals, etc., that the fish need to survive and the parameters are very different than the water the fish has been raised and kept in. Drop in a couple of flakes of fish food every day for about two weeks. Ammonia from this food will feed the growing colonies of bacteria. Do a 30-50% water change at two weeks. At this point, provided ammonia reads 0 on a test strip or with test drops, a couple of fish can be added. Keep a close eye on parameters and the general health of the fish and do partial water changes whenever nitrites edge outside of the safe zone. It takes about 36 days for a complete cycle.


There is a general rule of thumb that states you should have one inch of fish (from their adult size) per gallon of water. Again, this rule works well for small-medium community fish. Any fish six inches or over needs a tank that is no narrower than twice the fish’s length, and no shorter than four times the fish’s length. Always figure your stocking level by the maximum adult size of the fish. While it is true that some fish will only grow to the size of their tank, it is equally true that this enforced stunting will often drastically shorten the fish’s life and they will already be too large for the tank by the time they stop growing. For fish such as gouramis and oscars, only their head stops growing so that eventually their mouth will deform to the point that they can no longer eat. Some more aggressive fish may have particular space requirements to keep their territorial habits from bringing harm to other fish. Keep in mind that only about 20% of the aquarium’s capacity should be added at a time to allow the biological filter to catch up. Monitor the water parameters after adding new fish to ensure there are no potentially fatal ammonia spikes.


In general, fish are compatible with similar-sized fish of similar temperament and dietary habits. However, the tags in pet stores and short-term observation of the fish may not give an accurate picture of their temper. Always thoroughly research the fish ahead of time, and DO YOUR OWN RESEARCH. Just because someone works in a pet store, does not mean they know what they’re talking about when they give advice about fish. More often than not, pet store employees are just there for a paycheck and only know how to catch the fish for you. Pay attention to the strengths of each fish as well, as weak swimmers will have an unfair disadvantage against stronger swimmers at feeding times.


Aquariums need water 30-50% water changes 1-4 times per month. How do you know where your aquarium falls on the scale? You can come up with your own cleaning schedule by monitoring your water parameters. For the first month the aquarium is at full capacity, check the water every couple of days to ensure that ammonia and nitrites are at 0, and nitrates are at a safe level. Most test kits recommend keeping the nitrate below 40ppm through water changes, though invertebrates such as snails and shrimp should not be in water with nitrates over 20ppm.

When nitrates are approaching the upper limit for your tank, do a partial water change. The more water you change, the more nitrates that will be taken out, though too much can remove too much bacteria and cause an ammonia spike. Never change more than 50% of the water, and monitor the water for three days after the water change to ensure there are no spikes. Take note of how often you have to change the water and what percentage of change you can do without causing a spike. Once this is established, you need only test the water at every water change unless you have fish looking sick.

Do not change your filter cartridge with every water change. Most of the aquarium’s bacteria lives in this filter, so the cartridge should never be changed at the same time as a water change. Instead, remove the cartridge and rinse it out in a bowl of aquarium water, then put it back in the filter. Change the cartridge whenever it gets too much gunk in it to rinse out, or when damage occurs. Activated carbon only lasts about a week and is only necessary if you are trying to remove odors or medication; otherwise it is a needless expense.


All aquatic creatures require a variety of food to thrive. Most fish food off the shelves is sufficient to keep the fish alive, but it’s the equivalent of the cheapest dog food on the market. Supplement with freeze-dried, frozen, or live food in addition to flake or pellet food, and/or considering buying quality food online that doesn’t have fillers, color, and preservatives.

Fish are opportunistic eaters and so will continue eating and looking for food indefinitely. Any fish that doesn’t act hungry is an unhealthy fish, and just because fish are looking for food does not mean they should be fed. Think of a pet dog…just because it will eat a treat, does that mean it isn’t getting enough regular food? Fish can be fed anywhere from three times a day to once every other day, though juveniles (like most in the pet stores) should be fed no less than once a day. Never feed more than the fish can consume within two minutes.


Now that you have all the important basics down, you can consider some of the more aesthetic additions. Real and artificial plants are very popular in aquariums, though plastic plants should not be used with fish that have long, flowing fins such as bettas. Ceramic aquarium decorations are durable and beautiful, but be careful to buy decorations from trusted manufacturers. Some ceramic glazes contain lead which will kill fish, but anything that has a food-safe glaze should be safe for the fish. Resin or rubberized aquarium decorations should be added with caution, as many of these in cheaper brands have proven to be toxic. Lighting should be determined by considering the fish’s preference as well as those of any live plants in the aquarium.

There are several types of substrate on the market. The most widely known and available substrate is gravel, though it is less attractive and potentially dangerous to fragile fins compared to other options. Oyster shell makes a beautiful addition, though research should be done regarding its impact on water parameters as it does add calcium to the water. Sand is beautiful, comes in a variety of colors, and is easy to clean. The primary drawback of sand is that it can compact over time and harbor toxic gas bubbles, though this can be avoided by either manually stirring the sand once a week or by adding burrowing creatures such as Malaysian trumpet snails or khulii loaches.

The most important part of fish care is research. Make sure that you are very familiar with all creatures in your aquarium and have researched reliable sources for their proper care.

What aspect of freshwater fish care would you like to know more about? Please leave me a comment below with your question, and I will write a hub to answer it in detail.


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    • wychic profile imageAUTHOR

      Rebecca Mikulin 

      7 years ago from Sheridan, Wyoming

      Sure, I can do that :). Do you know what type of fish you have, or can you get a picture of it/them? Alternatively, if you can find a picture on the internet that looks like your fish I'll be able to identify it and will gladly write a fish care overview specifically for the fish that you have. Whether it's a livebearer or egglayer will determine how to tell if it's pregnant, and again I can help on that and will write you a hub tailored to the fish that you have. Hope this helps! :)

    • profile image


      7 years ago

      I would really like it if you guys can tell me how to take cere of ceartin types of fish.I don't know mine.also how to tell if your fish is preagnant

    • profile image


      8 years ago

      thanks i cant wait to get started!


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