Rule of thumb
“One inch per gallon” is a universally applicable principle for no matter how big the tank is. However, don’t just put one fish over 55 inches in your tank; that’s not how the rule works.
Essentially, we must consider fish species and temperament, as well as size and bioload.
Temperament and species.
Make sure there is no predation relationship in your tank; otherwise, it will be a bloody feast; then, think about which species you have or want to keep, because their temperament and compatibility will affect whether fish can coexist peacefully.
A 55 gallon tank can accommodate at least 10-15 African Cichlids. Some people have even crammed more than 20 Zebra Danios into a 55 gallon tank! So, simply do some maths on the types of fish you want to keep.
Then, the number of fish has a significant impact on this process; if overstocked, a toxic environment will undoubtedly harm the fish. Remember not to breed too many fish! If you want to test the water, an API Fresh Water Master Test kit will suffice.
Some of the best fish to grow in a 55 gallon tank. 3-4 fancy goldfish, 8 dwarf gourami, 2 male gourami, and 30–35 neon tetra. Each type of fish has unique requirements, so do your research before deciding which ones to add to your tank.
Concerning tank dimensions. A 55-gallon tank is medium-sized and rectangular in shape, typically 48 inches long*13 inches wide*20 inches tall. When decorations and devices are placed in the tank, the actual volume of the tank will be smaller than estimated.
A tank costs between $200 and $250; acrylic is more expensive than glass, costing between $50 and $80 more, not including other devices and decorations.
Some tank kits include a heater, filter, and lighting system for an additional $50-$80. A metal stand costs between $70 and $150, while a polished wood stand costs more than $150.
A filtration system capable of providing 220 GPH (gallon per hour) and adjusting the intake flow is required for a 55 gallon tank. A heater is also required if you are running a tropical system.
Maintenance. When positioning the tank, avoid direct sunlight and draughty areas first. A partial water change and removal of dirty water is required every two weeks, in addition to vacuuming the gravels and cleaning the glass.
Finally, when choosing a 55-gallon tank for your fish, take the time to get to know the fish you’ll be raising and do the tank maths.