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General Info

The Requirements Page and Health Page discuss several important points that are mentioned on this page. If you are interested in more info regarding the housing of tiger salamanders and metamorphosed axolotls, click that link.

Axolotls are not demanding in respect to their accommodation. It's important to bear in mind that an adult axolotl can reach anything from 18 to 35 cm in length (7-14 inches). Laboratories prefer to use minimalistic containers that barely allow the animals to turn around, like fish bowls. Each one is used to house a single animal, or a few are housed together in a container that approximates to a 45 cm long aquarium (18 inches).

For the enthusiast, the accepted minimum would be a 45 cm long aquarium (18 inch) for one adult. An example of an aquarium capable of holding several adult axolotls is shown in the photograph below. This is a good (if large) model on which to base your own axolotl aquarium.

1) Filter Inlet to External Power Filter (Eheim Ecco 2231);  2) 90 cm spray bar filter outlet;  3) Home-made plastic tank divider;  4) Floating plastic plants;  5) Piece of PVC drain pipe;  6) Large gravel/small pebbles (too large to fit in an axolotl's mouth);  7) Polystyrene board in black plastic;  8) Wooden board on a metal aquarium stand.

The Aquarium

This is a Marina aquarium of dimensions 120 cm long x 31 cm wide x 38 cm tall (48 x 12 x 15 inches)). The water depth is approximately 15 cm (6 inches). This is a good water depth, although it doesn't make much of a difference as long as the water covers the axolotls. For a display thank, a greater depth of water, and perhaps a much deeper tank, may be more desireable.

This tank contains approximately 60 litres of water (13 Imp gallons, perhaps 11 US gallons). The tank is mounted on a ~two foot tall brown-painted steel stand. Directly underneath the tank is a polystyrene board (used in walls for insulation, amongst other things) covered by a black P.V.C. bag. This board is very important because it serves to even out the pressure from the weight of the tank. The black plastic gives the tank a dark bottom, which serves to give the axolotls some comfort from excessive brightness (although this too isn't necessary).

The tank has been adapted so that it can be divided into three 40 cm long compartments. It should be noted that only one of the dividers is present in the photo. This is a home-made arrangement. The dividers are two sides of a polypropylene box that have been cut to fit the aquarium. They are held loosely by "right angles" of polyethylene from audio cassette cases (2 right angles on each side of each divider). I have cut a 2 cm length (1 inch) of Eheim filter tubing to protect the axolotls from the edges of these pieces of cassette case. The tank is divided to facilitate the separation of male, female, and juvenile axolotls. This prevents unwanted spawnings and predation. It also maximises the use of the space available. With regular maintenance, this aquarium could accomodate eight adult axolotls. I also like to think it has good Feng Shui!

Filtration

Filtration is not essential for axolotls, provided you're willing to change the water regularly. If you choose to use a filter, there are a number of options. Under-gravel filters, internal power filters, external "hang-on-the-tank" filters, and external power filters (also known as canister filters). I prefer the last type, but it is also the most expensive option.

Axolotls excrete a lot of waste. This is mainly in the form of ammonia (NH₃). Ammonia is a very toxic substance in its unionised form, NH₃, but this is in constant equilibrium with the ionised form NH₄⁺, and through the process of nitrification, it is converted into the less harmful substance nitrite (NO₂^-). This is carried out by the bacterium nitrosomonas. Another bacterium, nitrobacter, then converts this into the much more benign substance nitrate (NO₃^-). These two processes comprise the most important aspects of what is known as biological filtration.

Nitrate is a source of fixed nitrogen (i.e., not Nitrogen gas, N₂) for plants and fungi. Although it's not recommended to keep plants with axolotls (they tend to root them up and break them), plants will use the nitrate generated from a good filtration system. I discuss water quality and chemicals in more detail on the Requirements Page.

In my years of experience with aquarium filters and axolotls, I have found that it is important to choose a filter that is suited for filtering the aquarium's water volume. A large filter is not suitable for a small tank and will usually create far too much water flow in the tank. This is possibly the biggest cause of stress-related disease in axolotls. Obviously the tank shouldn't be like a river, but the actual water turnover through the filter shouldn't be much beyond what is required.

Too little "biological filtration" - roughly surface area for bacteria growth in the filter - is also a bad idea. However there is evidence of the phenomenon I will call "over-filtration", and this can be stressful to axolotls. By over-filtration, I mean too high a turnover and/or too much biological filtration. I will discuss this further on. This is more frequently encountered in the use of external filters, because they are intended only for large aquaria, yet novice keepers may utilise them with smaller accommodation. Over-filtration leads to water that is, aside from dissolved salts, like spring water - a rather hostile environment for axolotls.

The filter used for the tank pictured above is an Eheim "Ecco" 2231 (see the photo on the right). To my knowledge, it's their smallest canister filter, designed for aquariums from 60 to 100 litres (13-22 Imp gal, 11-18 US gal). It has a turnover of 300 litres per hour (66 Imp gal, 50 US gal). I've turned this down to about 150 litres per hour.

As you can see from the aquarium above, I've used a 3 foot long spray bar on the filter out flow. This was home-made from rigid plastic aquarium tubing, closed at one end by a square of Eheim green tubing pushed inside the tube. There are holes drilled about once every 4 cm. The reason for the length of the tube is to spread out the water flow, but also to provide very minor surface agitation through-out the tank. This is because the surface can become "dead" in the compartments away from a filter outlet. The water flowing from the spray bar trickles down the glass at the back of the tank.

Whether you use a power filter (internal or external), an under-gravel filter, or something above-board is up to you, but there are a few more things to keep in mind. If you don't use gravel, you may need a slightly larger filter to provide more surface area on which bacteria can grow. These bacteria, including nitrosomonas and nitrobacter, will make up the biological side of your filter, and need to have a sufficient surface area on which to grow in order to meet the demands made on them. You can buy filter media that is porous, and therefore has a surprisingly large surface area for bacteria. Eheim's "Ehfi-Substrat" is a sintered glass that performs this function. I use it in combination with the 2231's standard filter pads. Other companies like Fluval also supply similar filter media.

Finally, remember, you should "age" the tank for at least two weeks after filling it with water, connecting up the filter, and before adding many axolotls. The addition of a single small axolotl after initial setup will aid development of the bacteria on the filter media, in preparation for the addition of your other axolotls. Obviously, water should be dechlorinated with aquarium dechlorinator (or better still, left to stand for several days). More on water on the Requirements Page. Due to my experience (and impatience!), I rarely age my own aquariums. Instead, I add my axolotls immediately, but I clean the tank daily for two weeks. For the following few weeks or so I make slightly less regular water changes, in order to give the filter a chance to build up to full capacity.

Once your filter is established for a month or two, continue to conduct regular, if less frequent, water changes. I recommend changing between 10 and 20 percent of the tank's water volume every week, depending on how densely it is populated. I also advise that you "vacuum" up any uneaten food and unfiltered waste at least twice a week and replace the water removed. A small siphon is ideal for this purpose.

Gravel, Fine Sand - Substrates

There are pros and cons to using gravel. Axolotls have a nasty habit of getting normal aquarium gravel in their mouths, and occasionally swallowing it. This can be fatal because the gravel can cause blockages in the gut. Gravel-swallowing is a common problem, unless the gravel is very large (much, much larger than pea size). If you use an external filter like me, gravel tends to let debris accumulate in the tank, and so the filter has a hard time keeping the the bottom clear of solids. Since axolotls are messy, the filter may have its work cut out to deal with the excrement and waste food that accumulate in gravel. If you do use gravel, it's advisable to siphon the waste out of it - a "gravel cleaner" is ideal for this purpose.

In short, if you use normal aquarium gravel you risk killing your axolotl. It's rare but not rare enough to be worth risking. I recommend pebble-sized gravel, about 2 cm or greater in diameter. Alternatively, fine sand is also a good substrate, as it will not clog the digestive tract if ingested. It has been my experience that axolotls can't "grip" the bottom of a glass tank. This can be somewhat stressful over time. Plastic tanks don't suffer from this problem so much because no plastic is as smooth as glass.

The gravel used in the photographed aquarium is an "aggregate", coated with a polymer to prevent it from leaching minerals into the water. It comes this way and there are many types and sizes available.

Lighting

I don't have any specific tank lighting in the photographed tank, or any of my axolotl aquariums. The lid of the photographed tank is clear corrigated plastic. I have found axolotls to be sensitive to sudden marked changes in light level (turning a bright light on in a dark room).

Many successful axolotl enthusiasts use ordinary aquarium lighting - typically, a "hood" with a fixture for a fluorescent aquarium bulb and starter unit. Your local aquarium supply shop should be able to help you in this regard. In any case, lighting is essential for a display aquarium, and a must for an aquarium that contains live plants.

Temperature and Heating

The water should be kept between 14 and 20 °C (that's 57-68 °Fahrenheit). Anything below about 14 °C leads to more sluggish activity and a lower metabolism. At lower temperatures, axolotls will eat less frequently. They may even refuse food altogether. It should be noted though that axolotls don't seem to "hibernate" in the sense applied to most animals - they simply have reduced metabolism.

Above 24 °C, axolotls become stressed, and such warm conditions will usually result in disease if sustained for a several days. Temperature fluctuations of more than a few degrees Celsius in a 12 hour period (between night and day) can also be stressful. It's a good idea to keep the temperature stable on a day-to-day basis, even if it varies over the year with the seasons.

If you need heat, standard aquarium heaters used in fish aquariums are ideal for axolotl tanks. A heater set at 18 degrees Celsius is a good idea in a room that's very cool throughout the year.

Decoration

The addition of plastic plants, caves, pipes, etc., gives axolotls an added sense of security, as well as being attractive to the human eye. My axolotl setup in the photo may look very bare, but that's mainly for convenience of cleaning and feeding. For display purposes, I would employ a much more elaborate and eye-pleasing setup. By all means, keep your axolotls in such great splendour!

 

While not demanding, axolotls deserve to be well cared for, just like any other animal. Good luck with your aquarium plans. If you have questions about your proposed setup, why not talk to the people in the Axolotl area of Caudata.org's Forum? You will also find many ideas for axolotl aquaria there.