Zebra Danios behaving oddly

[commanderprimate]

Hallo there - hope someone can help.

Got three zebra danios about six weeks ago, placed into a 17 lt tank that had been cycling for 3 weeks. Up until a few days ago, they seemed absolutely fine, but then one vanished and was found wedged behind the filter (small stick on one). Sadly it was injured when I got it out and was dead the next day.

Remaining two fish seemed OK next morning, but then when I got home from work another one of the silly buggers had shoved itself behind the filter! This one swam off alright when I freed it, fortunately.

So, that's one bit of weird behaviour - five weeks they've had no inclination to stuff themselves up the filter and then suddenly it's all the rage with them. Also, one, which I think is a male, seemed to be chasing the others. Now the other female (I think), the one which went behind the filter yesterday is lurking behind a plant and not coming out.

Is it that the tank is too small for them? Is it a water quality issue? Or are they breeding perhaps?

Thanks for any advice.

Have you checked the water parameters? It sounds like you've got ammonia or high nitrates/nitrites that are making your fish poorly.

Also danios are shoaling fish and should be kept in groups of 6 or more to avoid stress related diseases and bullying.

Yes, they definitely need to be in a bigger group. They need a bigger tank too, they're very active fish. I would go 60+ litres for a group of 6. A larger group means that any aggression or squabbling is spread out over a larger number of fish and also the fish feel more secure.

It's unusual for a tank to cycle in only 3 weeks- how much ammonia were you adding while it was cycling? Did you get any readings during that time?

Ah, no, no readings. I'm beginning to think I've gone about this completely wrong - took advice from the guys at the fish shop, but they didn't mention anything of the sort.

I was looking to add more fish, to get up to 6 in total, but now I've read a bit more about appropriate tank size that doesn't seem sensible. So it may be that one fish was bullying the others and caused this odd behaviour then?

Not sure what to do now - there isn't really room to move up to a larger tank, unless there's one less than 30" in height but long anyone knows of?

I'll at least get a testing kit this weekend and see what I can do about the water quality.

Where are you based OP? I have a 2.5ft tank that's about 18inches high that is just hanging about in my shed since I stopped breeding my fish. You're welcome to it if you're not that far away. I might also have a big book on beginners fish keeping that I could scan you some stuff from if you've got any questions about things?

Mogz, I just looked on your profile to see where you're based and we're practically neighbours!

OP, there are a lot of tanks under 30" high- a 60 litre would be 24x12x12 inches. If you're not near Mogz then you could try Freecycle or similar, there are always spare tanks knocking around.