2 dead fish in a week?

[espo610]

my daughter has a small (not tiny) tank with 6 tiger barbs for over 3 months. water always treated, tested, and changed (1/4-1/3 not all) weekly. filter/heater/bubbler all working. suddenly one fish went belly up. thought of swin bladder issue. stopped feeding 2 days, but he died. checked to not overfeed, but a few days later another belly up, died next morning. i check water (ph, etc) all perfect. any ideas?

 

[Colin_T]

Can you post a picture and short 20 second video of the fish?

What is the ammonia, nitrite, nitrate and pH of the tank water?

Did you do or add anything to the tank the day before the fish started dying?

What are you feeding the fish and how often do you feed them?

The following link has some information about what to do if your fish get sick. It's pretty long and boring but worth knowing. I recommend printing it out and reading it in bed to fall asleep.
http://www.fishforums.net/threads/what-to-do-if-your-fish-gets-sick.450268/#post-3804819

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Do a 75% water change and gravel clean the substrate every day for a week or until the issue is identified. Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Make sure there are no chemicals, fumes or anything else getting into the tank.
Make sure nobody has any cream, grease, oil, perfume, or anything else on their hands when they do work on the tank or feed the fish.