Adding fish should never be done before the tank is set up and running properly.
So the aquarium is set-up. Water has been added and made safe for the fish to live in with a proper water conditioner. At this point, one of the most common questions is “How long before I can add fish to the tank?”
There are many opinions on the best time when adding fish for the first time; some people will even tell you to cycle the aquarium without them. Others will tell you wait weeks or at least a number of days. We do not believe that the first solution is one that is useful for the new aquarist. We don’t think the tank should ever be cycled artificially. Although, many so-called advanced aquarists suggest it as their preferred methodology. This protocol can be quite complex and difficult. You need to be close to a scientist to know how much ammonia to add, or even where to get it in the first place. Also, this method requires careful monitoring of the water characteristics and a good understanding of what the tests are reporting.
You are in the process of establishing a natural habitat, why expend the effort to start it artificially?
Some would make the case that cycling a new fish tank like this would be less stressful on the fish – since there are none used. In some cases this may be quite true, but only if the tank is overloaded in the first place. Follow the rules for stocking the tank properly and with suited species right from the start. When done properly, ammonia and nitrite stress should remain well within the limits of the initial fish you choose. You must, of course, pick a hardy species or two in the beginning.
Then you have the people who are telling you to wait a week or more before adding the fish. For the very careful person, where the environment must be perfect at all times, this may be a preferred option. This extended waiting period allows the aquarium to reach equilibrium and have a good period where the temperature is at the right level, showing the heater is properly set. But, we set up a tank to house fish, and like most people we don’t have as much patience as these perfectionists. A day or so is usually adequate for the tank to gain balance and the water to be deemed ready to support fish.
We do not, however, recommend adding fish by taking them home at the same time the aquarium is purchased. There are too many factors that can delay the aquarium installation. The fish don’t need the stress of waiting in the bag for the tank to be installed and filled. It often takes about 24 hours or so for the temperature in the aquarium to become stable, and the heater properly set for maintaining the desired level.
The tap water, for the most part is made capable of sustaining life at the instant when the water conditioner is added. In the case of a new installation, a small grace period should be allowed for the various water characteristics to stabilize and find their equilibrium.
We prefer to recommend that you can be adding fish about a day – 24 hours – after the water has been added to the aquarium – with the water conditioner properly dosed to remove chlorine and allow any heavy metallic ions to be neutralized. This gives time to ensure that the temperature is right and the water has had time to reach an equilibrium as far as other characteristics. The 24 hour grace period also allows the filter to take any suspended particles, such as gravel and media dust out of the water before the fish enter the system.
If plants are being kept, they, on the other hand, can be added as the ecosystem is being created. It is easier for them to be placed in position as the tank is filled. They are not as susceptible to the tap water as fish, and are usually quite hardy in the beginning as well. A somewhat extended waiting period in the bag also does not seem to do them much, if any, harm either. If there is a delay in the set-up, they are not going to be hurt, which is not the case when live fish are waiting in a sealed bag to be released.