Guppies dying one by one...

[dylema]

We're still new to aquarium keeping so I thought I'd post this here.
We have a 16L tank with 4 zebra danios (will get a couple more soon) and a couple of guppies. Danios are fine. All tank levels are fine (nitrate/nitrite virtually zero, ammonia 0.3ppm). But one by one the guppies are passing away I don't know why, they seemed fine, happy, active, colourful, eating and pooing. They sort of hover on the bottem and seem a bit listless and eventually we find them dead. There's only two left now and they are on the way out...
Any suggestions?

 

[Discomafia]

ammonia should be 0 in a cycled tank, as well as nitrite, not virtually zero. I can safely pressume that the reason the fish are dying is because of this high ammonia reading, so first thing to do is do an immediate water change of 40 or 50%... Also 16L is only 4 gallons and they need to be in a school of 5 in a 20 gallon tank minimum. So no new fish, and immediate water change, followed by either a new tank or getting rid of your danios to a lfs or friends or something...