I have just added 2 new zebra Danios to my tank from my LFS.
First Danio had been in for a week, after 3 months to get water right on a fishless cycle.
At first the 2 newbs shoaled together. Now they have been circling each other quite aggressively for several hours. They completely ignore the original resident.
As they are shoaling fish I did not expect this.
Any ideas what they are doing? Are they fighting over who is to be fish king (or queen)
Does anyone know how you tell male frmm female in this species?

Hi there!
What's the size of your tank and inhabitants in it?
There are many reason for fish to be aggressive but if they're chasing down their own specie, it might be breeding time.
Take a look at this caresheet, Female is rounder and bigger than male one (male is really slim) Of both of your fish is the same sex, it's might be food or space problem. Keep watching them and see if they can make it out themself :)
http://www.fishkeeping.co.uk/modules/ ... esheet.php?caresheetID=20

You need some more of them. They are happier and behave better in big groups. Any argy bargy gets shared out and dissipates. Minimum 6, more are better. Have you got the tank space for this?

Eta: just notced they are in your 30l biorb ... they will be miserable in that. Danios are fast, athletic swimmers, needing at least a 2 foot tank, longer is better. It I were you I would get them into your bigger tank asap (if you use the biorb ceramic media and sponge in the filter at first then gradually swap it over for the filter's own media you will not need to do another fishless cycle). Then use the biorb for shrimps, it is not really satisfactory for any fish ...

Hi Cathie, I have some question.
I have 10 danios in a 60l tank ( 50cm long). Do you think enough? They seem to be fine and happy about it.
By the way, danios are cold water fish but my fish is living at 28C... should I gradually lower the water temp or leave it be?

Hi,
New to forums so bear with me.
Thanks for replies
Have a look at my profile. it's got all my tank info on.
With your advise I have worked out I have 2 females and a male.
My original occupant looks like juvenile female.
All the rushing around was courtship! It explains the rapid inflation of the two females too. They were full of eggs.
They seem to love the live plans I have added and have spent all last night spawning in them. The smaller female did a lot of off menu egg eating.
They have all settled down now.
The only unpleasant surprise has been an overnight nitrite (N02) spike to around 2ppm.
I am going to do a 20% water change now. I can tell you what water treatments I have here. Do I add this as a new topic?

Might be an idea to get the best exposure for your question, but essentially oif you have a nitrite spike the way to deal with it is by daily (or even twice daily) 25% water changes until it settles back to 0.

There are two other things that can assist in protecting from the effects of high nitrite. One is to use Seachem Prime in a double dose for the whole tank at each water change. The other is to add salt to the water. You can use aquarium salt or cooking salt, sea salt as long as they don't have any other additives such as anti-caking agents.

In the 30 litre Biorb dosing at .1 grams per litre should be enough - so 3 grams or half a level teaspoonful. When you do a water change, use that same amount in proportion to the amount of water changed. If you need to top up for evaporation at any time, don't add salt, as the salt in the tank won't evaporate.

Hi Noodle,
thanks for salt info. (salt at home has caking agents)
Adding salts converts the nitrite to a less toxic form, is this right?
Do you mean add salt and Seachem Prime or only one option?
I will check out my LFS now.

Use one or the other. If you can't get Prime locally, use salt, but I recommend switching to Prime as your standard dechlorinator as it's very economical in use, can detoxify ammonia and nitrite in an emergency and is known to have no effect on common meds, particularly eSHa products. It's usually available on eBay at a reasonable price.

Quote:

I originally had my danios in a 2 foot tank (60 cm) - I was just looking after them while another member, natterjack, moved house. I eventually ended up keeping them and moved them into a 100 cm tank and the change was quite dramatic. So I would say if you can move them do, and also into a cooler tank, say in the 20 -26 range

Too bad, the longest tank I have is 70cm(200l) :( but that tank is a tropical one with temp always above 27 (I keep tetras there). I've managed to lower the temp in my tank with floating ice packs but the lowest I've reach is only 25(the temp change gradually) but once the ice pack cool down and I don't add another one immidiately, the temp raise back to 28 or even 29 in just few hours. I'm going to make lots of ice packs