When keeping an aquarium everyone wants to know just how many fish they can keep in it. There is a general rule of thumb that is 1” of fish for every gallon of water in the tank. This rule isn’t something that is set in stone and it can be broken. There are three big factors that can help keep more fish than that general rule allows.
The first factor is the filtration that is set up. Filters are meant to remove the ammonia and clean the water. You can get different sizes of filters for how big the tank is. One common practice is getting a filter that is fit for a tank that is larger than what they actually have. For instance, I have a 45 gallon tank but I have a canister filter that is meant for a tank with 100 gallons. Having the bigger filter results in more waterflow and more times the water is passed through the filter within an hour. Then the more times it is passed through the cleaner the water is.
The second factor is how heavily the tank is planted. Plants are able to clean the water by absorbing some ammonia and giving off oxygen in the tank. If the tank has a lot of plants, then there are more places for the water to be cleaned. If the tank has fake plants, then there isn’t that biological filtration. Having a heavily planted tank helps clean everything in there cleaner.
The third big factor is how often you do maintenance to the tank. Having a lot of fish means there will be a lot of waste. If that waste isn’t removed it will become lethal to everything in the tank. The easiest way to remove that waste from the tank is by doing water changes. It is a common practice to do a 25% water change every week. However depending on how many fish are in the tank and the filter and how many plants this number will change. I have had my tanks understocked before so I would only do a water change about once a month. I have also had it where I had more fish than I should and would do a 50% water change every week.
To determine if what you’re doing is healthy is by doing water checks. It is important to check the ammonia and nitrite at least once a week. Whenever those levels are either above or close to the dangerous ranges, a water change should be done.