Okay so I had five Tiger Barbs in a community tank. They killed two of my fish. I moved them into a smaller five gallon hexagon tank. Four of them killed each other. I found them at the top belly up with no fins at all and bites taken out of them. So there were two fish left a Spotted Green Puffer Fish and a Tiger Barb. I cleaned the tank two days ago and put all of the necessary chemicals in for making tap water safe. My tank was full of algae. So full that the bottom of the tank looked like it had grass. So, I did a 93% water change. I then returned the fish. Oh I forgot to mention the Green Spotted Puffer Fish was dead when I went to clean it. My first fish. :( Anyway I returned the Tiger Barb and tonight when I went to give them before bed meal, I found him floating upside down with gills still moving and he looked perfectly mobile. So I hurried and moved him into my community tank and after about thirty seconds of upside down floating he was right side up and fine. What was wrong with him or the tank or both??

Honestly, the green puffer is a brackish water fish and should be in a single specimen tank at least 30 gallons. They are not suitable for community tanks and may cause harm to your other fish.

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What probably caused your problem however was the major water change. That will change your pH levels, your temperature and other bits and pieces of your chemistry.

I highly recommend you research your fish before you put them in your tank. Just because a person works in a fish department at a store does not mean they know what they are talking about.

Also, tiger barbs should be kept in groups of 8-10 individuals if you don't want them picking on other fish.

EDIT: I wouldn't put barbs in with angels for the fact that they tend to be fin nippers, especially if they aren't in a school where they can just harass each other. They tend to nip off the long whiskers of the angels. Alternatively, your angels might become aggressive with the smaller fish. Tiger barbs are a common fish, and unfortunately, they are not right for many peoples' tanks. :( Sorry.

The puffer is going to destroy any living creature in that water...if it is bigger expect fins to be missing...but here is my GSP in a 30gal by himself

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http://www.youtube.com/watch?v=CxDKwL2rWjM

http://www.youtube.com/watch?v=CxDKwL2rWjM

Your fish might be attacking one another. I had the same problem with my fish. Try to put them in individual tanks. For the Tiger Barb, it might be because the water was too cold and he passed out. Or his spine (spine?) might be slightly bent.

Did you wash all the pebbles and furniture in the tank. It could be it could be dirty or you used too much soap and it went into the water.

maybe the temperature was too low, or maybe you put too much chemicals in..

Check pH and ammonia or nitrate levels