Aggressive Zebra Danio

[Jane47324]

I have a fairly new 30 gallon(UK) tall tank with 4 zebra danios, 4 glow tetras and 10 very small cardinals.
Water specs: Temp 25C, pH about 8, Ammonia less than 0.1mg/l, Nitrite less than 0.1mg/l, Nitrate about 10mg/l
I have been managing the nitrate levels by 25-30% water changes every 2-3 days, pre warming the water to keep the temp steady.
Apart from the fact that my cardinals all seem to have a kamakazi desire to swim up the syphon - one very near loss has made me super cautious about covering the end.
This morning, after feeding, one of my zebras started chasing another, they swam around each other very fast, apparently 'nipping' each other at the base of the tail and evenentually one was driven away. The 'aggressive' one started chasing other zebras - 'he' hasn't bothered the tetras.
What should I do, please?

 

[JonE]

I have a fairly new 30 gallon(UK) tall tank with 4 zebra danios, 4 glow tetras and 10 very small cardinals.
Water specs: Temp 25C, pH about 8, Ammonia less than 0.1mg/l, Nitrite less than 0.1mg/l, Nitrate about 10mg/l
I have been managing the nitrate levels by 25-30% water changes every 2-3 days, pre warming the water to keep the temp steady.
Apart from the fact that my cardinals all seem to have a kamakazi desire to swim up the syphon - one very near loss has made me super cautious about covering the end.
This morning, after feeding, one of my zebras started chasing another, they swam around each other very fast, apparently 'nipping' each other at the base of the tail and evenentually one was driven away. The 'aggressive' one started chasing other zebras - 'he' hasn't bothered the tetras.
What should I do, please?

We had the same problem with 1 of our Danio try adding another 1 or 2 it worked for us, they are a shoaling fish and do better in larger groups I think 5 or 6 is the recommended minimum.

Cheers

Jon

 

[Noahs ark6]

I had the same problem when i got some danios. Like above, try adding 2 more

 

[the_lock_man]

I don't think there's a huge amount you can do - you can't exactly put it on the naughty step. Adding more will spread the aggression out a bit more, but danios are feisty towards each other like that.