When to add new fish?

Neufusion

I have 3 tiger barbs in a 26 gallon tank which has been running well for about 7 days.

I am anxious to add new fish. :)

Is it safe to add a new fish or two now?

How slowly should new fish be added to avoid a huge ammonia spike?

Lonewolfblue

7 days is not long enough to cycle the tank. Do not add any more fish until it cycles. You will get an ammonia spike, may take a week or 2. Then after that, you will get a nitrite spike. After both ammonia and nitrite go to 0ppm, you are cycled, and can start adding fish, maybe 3-4 fish every 2 weeks, til you are stocked. Remember, cycling can take 6-8 weeks, sometimes longer, sometimes shorter.