Poorly guppy?

[Wraholt]

Hi all

Our daughter got a tropical tank for Christmas. She has 6 cardinal tetras and two male guppies. One guppy seemed to be getting bullied by the tetras yesterday and then he spend most of his time “hovering” towards to top of the tank. Today he is staying on the surface. On the odd occasion he has moved, he is swimming by only using his side fins, he doesn’t use his tail and seems to shake his body. His tail is bedraggled and even when he swims he seems to stay at a 45 degree angle.
Have tested the water and all looks as it should.
Any suggestions?
Thanks x

Edit - every time I upload the picture, it gets flipped on its side!! Can’t get it the right way up

 

[fishwonder]

How did you cycle your new tank/filter? This take 3-8 weeks before any fish should be added. Click here on how to perform Aquarium Cycling.

 

[Barber]

Hi. I had this in a new tank and lost some guppies. My local fish shop inspected one of them when he was ill - said he had clamp fin, probably due to stress. They also tested a sample of my water and said it was ok. They recommended a 'General Tonic' treatment. I haven't lost any since.
How big is your tank (e.g. Litres).
The new fish you have added should be able to start your nitrogen cycle for you, but don't add any more and only feed sparingly.
I would recommend googling the nitrogen cycle in aquariums.
What type of filter are you using?