Aggressive Zebra Danio

[Wayne Eaton]

Hi guys

Looking for a bit of advise. I new tank which I set up for my daughter. Its only 25 litres.

Introduced 2 zebra danios, 3 Barbs and 2 mountain minnows, I did ask if they were okay together and the guy in the LFS said yes. All has been fine for a week but this morning I noticed one of the minnows wedged down the side of the filter so i got him and but he seemed pretty stressed, not swimming quite right.

Then noticed one of the Zebra Danios nibbling at it, the other minnow and the other Danio, it seems to leave the barbs who are totally fine. Feel a bit crappy now and not sure what the best course of action?

I'm feeding them once per day, any advise?

 

[Essjay]

Hi, welcome to the forum.

I'm afraid the guy at the LFS did not give you enough information. Zebra danios, barbs and white cloud mountain minnows are all shoaling fish, which means they should be in a group of at least 6 of the same species, with more being better. When there aren't enough of them they get stressed which usually results in either the fish becoming timid and hiding, or becoming aggressive.
Do you know what type of barb you have? Some species are pretty aggressive while others are not. If you don't know, post a photo and we'll ID them for you.

I'll bet the LFS guy did not mention cycling the tank either. Very few of them do. This means growing two colonies of bacteria in the tank which 'eat' the ammonia made by the fish, and the nitrite made from the ammonia by the first set of bacteria. Both of these are toxic to fish, but it takes several weeks to grow enough bacteria so until then we have to do water changes, lots of them, to keep the fish safe.
Reduce feeding to once every two or three days. This will reduce the amount of ammonia made by the fish. And fish don't need as much food as you'd think.

The third thing the LFS guy didn't tell you is that the tank is too small for each of the species you bought, which means that upping their numbers to 6 each is not a good idea.


What to do.

First of all you need a test kit, one that tests for ammonia and nitrite. Liquid testers are better than strips, and there are master kits containing pH, ammonia, nitrite and nitrate. Until you get the testers, you need to change about 75% of the water every day. Once you have the testers, test daily and do a big water change every time you see ammonia and/or nitrite above zero.
Then you need to think seriously about the fish. There are basically two alternatives.
Take the current fish back to the shop and get fish suited to the size of the tank. This is basically one betta. That's all, nothing else with it.
Or get a bigger tank. I'm sorry to tell you but despite their small size, zebra danios need a tank at least 100 cm long because they are such fast swimmers. Being in a tank that's too small will also stress them which could make them more aggressive.



Here is a link https://www.fishforums.net/threads/cycling-your-new-fresh-water-tank-read-this-first.421488/ The first part explains better than me what cycling is, though as you have fish, the second part does not apply.

And as you have already discovered, never believe what a shop tells you. Most of them don't have a clue and will make up anything to get a sale. Ask on here first