Veterinarian Buffalo -Veterinary
My local Buffalo veterinarian gave me some good tips on adding new fish to your existing aquarium. Quarantine tanks are a good idea, but few people have them. If you, like 99% of hobbyists, are putting your fish directly into your community tank, be patient. Float the bag for 30 minutes to equalize temperatures. Now, you have three options.
You can dump the bag and water right in. Most people do this. The water can carry disease though.
You can net the fish out, and put them into the water directly. You can shock a fish this way, as the water chemistry and pH can be different. You reduce the disease potential and increase the danger of shock.
You can remove some store water and add your tank water to the bag, slowly, until the two are the same or similar, then net your fish out. This way is slow, but safer. You dump the water outside the tank.
Before you release your new fish, turn off the tank light, or put some in the tank. If the established fish are busy or distracted, they'll be less likely to pick on your frightened new arrivals. Overcrowded tanks lead to diseases and heavy maintenance work. The aquarium cliché of "one inch of fish, not counting the tail, per gallon" is good for tetras in well-filtered and maintained tanks. Fewer is better, although it's hard for newcomers to the hobby to get around that. However, an inch of goldfish could hold a pile of stacked up tetras! One big-bodied fish like a goldfish will fill a 20-gallon on its own. You have to use your judgment, and stock as lightly as your desire to acquire new species will allow.