What is an Unfiltered Tank and How do I Cultivate One?

If you have done any basic research about freshwater aquariums, you have probably learned about the importance of maintaining high water quality. The cleaner your tank water is, the happier and healthier your fish will be. In most cases, maintaining high water quality requires you to outfit your tank with a filtration system. A rising trend in the aquarium hobby, however, is focused on tanks that do not require any kind of filter system.

A healthy and thriving unfiltered tank is possible to achieve, but it will take some forethought and planning. In this article you will learn the basics about unfiltered fish tanks and how to cultivate one for yourself.

Tips for Maintaining an Unfiltered Tank

The key to maintaining an unfiltered tank is to two-fold. First, you must carefully choose your tank inhabitants to make sure that they will not only survive in an unfiltered tank, but that they will contribute to the ecosystem. For example, live aquarium plants will act as filters by converting the CO2 produced by your fish into the oxygen they need to breathe. Having plenty of live plants in your unfiltered tank will help to keep the water quality in your tank high enough for your fish to survive.

Second, after you have set up your unfiltered tank you need to take certain steps to maintain high water quality. Stocking your tank with plants alone is not enough to accomplish this goal – you will also have to perform frequent water changes and be very careful about any additives you use to treat the water. Liquid fertilizers and medications, for example, can throw off your water chemistry and, once your water quality declines, it can be hard to bring it back up. Always research things before you add them to your tank and, if you decide to use them, follow the dosing instructions carefully.

In order to keep your unfiltered fish tank clean, you also have to think about ways to reduce algae growth. Keeping live plants alone will help with this because the plants will compete with the algae for nutrients. To further reduce algae growth, try to stick with low-light plants because excess light is one of the main causes of algae growth. Avoid placing your tank near a window that receives direct sunlight and keep it away from heating and cooling vents – this is especially important if you plan to maintain your tank without a heater as well. In order to keep your live plants alive, however, you will need to use some kind of nutrient-rich substrate to supplement the nutrients your plants get from the waste produced by your fish.

The Best Species for Unfiltered Tanks

When it comes to stocking your unfiltered tank, you need to think carefully. Because you don’t have a filter in place, your water chemistry is likely to fluctuate a little bit so you’ll need to pick hardy species of fish. You also want to make sure that the fish you choose fill some kind of role in the tank – bottom-feeders like Plecostomus and corydoras catfish are great options because they will help to clean up accumulated detritus and debris. Below you will find a list of some low-maintenance fish that might be a good fit for an unfiltered tank:

1. Paradise Fish (Macropodus opercularis) – The paradise fish is actually a type of gourami that can be found in freshwater habitats around East Asia. This species can survive in warm or cool waters and it is very hardy in fluctuating water conditions. Paradise fish grow to a maximum around 2.2 inches and they are very brightly colored.

2. Common Plecostomus (Hypostomus plecostomus) – The plecostomus is a species of armored catfish commonly kept as an algae eater. This species is fairly hardy and it does a good job cleaning up the tank while young but it tends to become aggressive and lazy as it gets larger. As such, this fish might be a good short-term addition to an unfiltered tank but should eventually be moved to a larger filtered aquarium.

3. Fancy Guppies (Poecilia reticulate) – The fancy guppy is a small but hardy species of fish that tends to breed readily in the home aquarium. These fish only grow to about two inches in length but they come in a wide variety of colors and patterns. Guppies prefer warmer temperatures between 78°F and 82°F, however, so they may not do well in an unheated tank unless the ambient temperature in the room is warm enough.

4. White Cloud Mountain Minnows (Tanichthys albonubes) – White Clouds, as these fish are more commonly known, are a great starter fish and they do well in unheated tanks because they are naturally found in cold mountain streams. These fish remain small, growing to a maximum around 1.5 inches, and they prefer cooler temperatures between 64°F and 79°F. White Clouds are very peaceful fish as well, so they get along with other peaceful species.

5. Neon Tetras (Paracheirodon innesi) – Neon tetras are one of the most popular species of freshwater aquarium fish because they are hardy and easy to keep. These fish can be found throughout parts of South America and they are easily identified by their silver bodies with an iridescent blue horizontal stripe over a horizontal stripe of red. Neon tetras only grow to a little over 1 inch in length and they prefer soft, acidic waters on the cooler end of the temperature scale (about 77°F).

6. Bronze Corydoras (Corydoras aeneus) – The Bronze Corydoras is a species of armored catfish that can be found throughout South America. These fish grow to a maximum size around 2 ¾ inches and they have broad bodies with barbels on their mouths. Corydoras catfish are bottom-feeders so they will help to clean up accumulated debris from the bottom of your tank. One thing to be wary of with corydoras is that they do not have scales so they may be more sensitive than other fish to certain medications and other additives.

In terms of plants to choose for your unfiltered tank, you want to choose species that do not require high levels of light and which do not grow too quickly. Some examples of low-maintenance aquarium plants include java fern, undulata, anubias, and red cryptocoryne. Even though these plants are low-light species, they still need about 10 to 12 hours per day of full-spectrum lighting – the term “low-light” only refers to the wattage of the lighting they need. You also need to be mindful of the fact that while aquarium plants produce oxygen from CO2 during the day, the process switches at night and they will consume some of the oxygen in your tank. If you avoid planting your unfiltered tank too heavily, this shouldn’t be a problem.

Keeping an unfiltered tank is a challenge, but so is maintaining any freshwater tank. If you are willing to do the research and the work to make your unfiltered tank a success, however, it can be a very enjoyable experience. The information and tips in this article should be more than enough to get you started with your own unfiltered tank.