Zebra Danios Are Aggressive

[Echinoderm]

I had 4 zebra danios in a 15 gallon tank to help cycle. Yesterday, one died. I think it got stuck in a plant, but I'm not sure.

Today, the three started acting extremely aggressive. They are chasing each other around the tank. They tried to attack my test strip, and they ate like piranas.

Is this water chemistry? Chemicals are a little bit high because I have new tank syndrome. It is a new tank after all.

They were so peaceful before...

 

[SBL]

Well, the number dropped and Danios need to be in groups of atleast 4 or they become aggressive . I have a Giant (actually is almost the same as a Zebra). and He was part of a quad but 2 Jumped out and they became aggressive so they went into our 500 USG pond. Now, only one is alive andnhe is currently inside and is aggresive but, won't attack aggressive fish or fish that aren' afraid to brawl with him(*cough*Betta*cough*)

 

[Haych]

as far as i'm aware, and have had experience with them, i would not keep danios for this reason.

i had 5 or 6, and they used to dart across the tank bullying anyone in the way.

i would never have them again, but i wouldnt say its the water, i would say its just them

 

[aly_starh]

I have 3 zebra danios, there constantly swimming Very active fish.

Todoy one of my tetras died and they started attacking it, they have never been aggressive to the other inhabitants, (gourami, tetras, corydoras)

 

[Curiosity101]

It'll be a mixture of a few things, the least of which being the water chemistry.

15gal is too small for danios. They are EXTREMELY active fish, and anything below 80cm in length will be too small for them. This causes stress, which in turn causes aggression.

A group of 3 will lead to more agression as they are unable to form a proper hierachy.

The water chemistry will have killed the danio that died. And just cause you have a new tank, doesn't mean you have to suffer from new tank syndrome.
New tank syndrome is cause by the filter not being cycled. For the filter to cycle you need an ammonia source. This can come from fish or from a bottle (ie. bottle of household ammonia).

If you want to get your tank ready for fish without going through 'new tank syndrome' you can do something called a fishless cycle. Which basically means you put ammonia into the tank, and the bacteria that make the ammonia safe can grow on that. Then there will be lots of bacteria ready for when you go to buy some fish

Sadly you already have fish so you are fish-in cycling. This means that there aren't enough bacteria to use the ammonia the fish are creating. This leads to excess ammonia and nitrites in the water which is very toxic to fish.
I would recommend a water change (50% at least), immediately, to avoid anymore losses.

Also what are you test results exactly? I know this wasn't your original question, but I'm guessing you don't want to loose more fish? If you don't then we can help...

 

[Echinoderm]

It'll be a mixture of a few things, the least of which being the water chemistry.

15gal is too small for danios. They are EXTREMELY active fish, and anything below 80cm in length will be too small for them. This causes stress, which in turn causes aggression.

A group of 3 will lead to more agression as they are unable to form a proper hierachy.

The water chemistry will have killed the danio that died. And just cause you have a new tank, doesn't mean you have to suffer from new tank syndrome.
New tank syndrome is cause by the filter not being cycled. For the filter to cycle you need an ammonia source. This can come from fish or from a bottle (ie. bottle of household ammonia).

If you want to get your tank ready for fish without going through 'new tank syndrome' you can do something called a fishless cycle. Which basically means you put ammonia into the tank, and the bacteria that make the ammonia safe can grow on that. Then there will be lots of bacteria ready for when you go to buy some fish

Sadly you already have fish so you are fish-in cycling. This means that there aren't enough bacteria to use the ammonia the fish are creating. This leads to excess ammonia and nitrites in the water which is very toxic to fish.
I would recommend a water change (50% at least), immediately, to avoid anymore losses.

Also what are you test results exactly? I know this wasn't your original question, but I'm guessing you don't want to loose more fish? If you don't then we can help...

This happened awhile ago so I don't have the test results.

Yes, I know exactly why I have new tank syndrome. It's a new tank and the fish are cycling. I know what cycling is. I don't care if they die. It's been exactly two weeks now and I've done a water change. Everything seems to be fine. I think the tank is completely cycled. The fish are a little better.

I'm getting Dwarf Puffers in a few days.

 

[sebseb]

controvesial

 

[onebto]

Since reading another one of your posts I have decided to withdraw my comments and advice and as i wish to remain a member of this forum I will refrain from posting the low opinion I have of you.

Regards onebto