If you don't keep juveniles in the tank that are different in size, things will be fine. But even if you have two different sizes, you can keep them in separate tanks until they grow up to be similar and then keep them together. Keeping only one Axolotl is probably the best, but it is up to you.
You'll need to keep your axolotl in an aquarium enclosure with slightly cooler than room temperature water, a water filter, substrate, and very minimal tank decor. They do best in 20+ gallon enclosures and should live alone, as they can be territorial.
Axolotls are not a social species, so they don't need a friend to be entertained. That being said, it is perfectly ok to house axolotls together, as long as they are roughly the same size. If one axolotl easily fits into the other's mouth, chances are it will end up as a snack.
Housing Your Axolotls
A 10-gallon tank could work fine for an adult axolotl, but they do produce a significant amount of waste, so you may want to go with a 20-gallon tank that will stay cleaner for a longer time.
In the wild, axolotls are solitary animals, and so are happy being kept on their own. If multiple axolotls are to be kept together, enough space should be given for each one to have its own area away from others. Axolotls are messy animals, and sensitive to poor water quality.
Each Axolotl requires a certain amount of space to survive and live. Buy at least a 20-gallon tank for a single axolotl. If you want to keep two axolotls, you must double the size and get a 40-gallon one. That's all you need to extend it by 20 gallons for every additional Axolotl.
To reiterate, the only way to avoid these outcomes is to either have a secondary tank set up in case you need to separate the axolotls, or only purchase adult axolotls that have been sexed, and only house same sex axolotls together. There is no risk in having multiple males or multiple females together.
Axolotl care requirements are minimal, and provided temperature and water flow are well controlled, they are hardy, easy-to-care-for captives that breed readily in captivity. It is difficult to think of a more unusual display animal than the axolotl, and its bold and tame nature makes it an interactive pet.
Axolotls and goldfish cannot be kept together as tank mates or in a fish tank. The creatures require different basic living conditions and water parameters, and goldfish could stress and injure the Axolotls by nipping at their tails and gills.
Lifespan: In the wild, axolotls generally live 5-6 years but can reach 15 years in captivity. Breeding: Axolotls reach reproductive maturity after their first year of life. In the wild, axolotls breed once a year between March and June.
Axolotls tend to be fairly bold and are perfectly content to move about their tank as they're being watched by their humans. Some will come up to the side of their tank when a person is there observing them. However, they aren't particularly social animals and don't require any tank companions.
Can you keep axolotls with fish? The answer, surprisingly, is yes — you just need to choose your fish carefully. One thing to keep in mind when keeping fish with axolotls is that those long flowy gills can start to look like food to just about any fish who's hungry enough.
Baby axolotls should be fed daily to support their growth and development. Adult axolotls need to eat less often, perhaps one or two servings every other day. In fact, they can do just fine for up to two weeks without eating any food (although this shouldn't be tried at home).
Cats, dogs and other common pets
There are no restrictions on cats, dogs, guinea pigs, rats, mice and axolotl (walking fish).
“They can be great pets, but they aren't great pets for everyone – and children need to know that they can't handle an axolotl as they're very delicate and they can get injured. They also need a very quiet home with a lot of space – children aren't known to be very quiet”, Dr Beattie correctly says.
Humans can touch an Axolotl anytime. There is nothing on their skin that can hurt a human. Keep in mind that before you touch an Axolotl, make sure to wash and disinfect your hands. Try to avoid transferring any type of bacteria or contaminants from human skin to the Axolotl.
What Do Axolotls Eat? Axolotls are carnivorous predators that usually hunt at night. They use a suction method to suck up crustaceans, mollusks, insect larva, worms, and sometimes small fish. They also may suck up bits of gravel to help grind up their food and make it easier to digest.
The water depth should be at least 15cm deep and needs to be kept at between 14 and 20°C. If the water gets too cool the axolotl will become sluggish and eat less frequently and if too warm it will become stressed. A standard aquarium heater set at 18°C is ideal for an axolotl tank.
If an axolotl is out of water for more than five minutes, it'll begin to take damage and die.
Axolotls require brackish water — a mix between fresh and salt water. This is one of the main reasons that Axolotls are not recommended for first-time aquatic pet owners. It is recommended that owners be very familiar and comfortable with basic freshwater aquariums before starting with Axolotls.
As Eva said - Axolotls are not territorial and having more than one males in the tank would be no more a problem than having more than one Axolotl at all (I am not common with the measures of a "55 gal long"). I provide them some hideaways and lots of plants so they would not have to see each other all the time.
Therefore, if you can accommodate, it is always recommended to choose a 20 gallon or 30-gallon tank because the ammonia and nitrate levels in these tanks would be controlled. Also, your axolotls would get enough room to explore and play around.