I have been keeping finches for about 2 yrs and had a large healthy stock .I bought one from a shop and I lost half my stock in a week,I put it down to the new bird being sick and infecting but it has happened on three more occasions now I have none left . Any ideas?

Did you have any tests done at all?

My first thought initially would be coccidosis or mice,

As the bird that you introduced was from a petshop then it could be a disease which had been brought from their..
Many birds can live for years without showing symptoms of these diseases and only when they get stressed (like a move does it then become apparent)
I learnt the hard way about quarentine and birds when I lost over 2000 pounds worth of birds in less than a week..
Quarentine for a period of 2 weeks should be took out with any new bird purchased..

If your birds were fine and healthy until you introduced the new bird then the chances are it is a disease brought from the shop..

What I do for quarentine is I will take the new bird to a place away from any other birds you have , and disinfect hands every time I go anywhere near the cages... I will then take 1 bird out of my own collection of birds and place it either in a cage next to the new bird or in the same cage as the new bird,

This way if the new bird has any illness that she is living with but can spread about without her showing the symptoms then the new bird will get the disease and get ill within the time frame of the 2 weeks , this way only 1 bird loses its life and the rest are saved,

I would have a word with the petshop see if they have had anything happen or reports (they will prob deny it though) but they don't think about it if they are not told...

If there are any piles of poop that are in the shed/aviary/ etc scrape them up and pay for them to be tested by the vet.. they can tell a lot of stuff fom just poop..
Also if you have any bodys left that are under 2 days old you may want to get 1 tested also...

I feel for this situation and can empathise with you completely,
The main key here is to now scrub and disinfect the whole area where you kept the birds,
Spray it with mite spray, I would use virkon s for the disinfectant (defra approved and gets rid of most bird diseases! )
You must no tleave any place in their uncleaned... everything has to be scrubbed with disinfectant so as to get rid of the disease and stop it spreading..

I really do hope you find the causes..

And also can I ask if their were any symptoms of the birds before they died , i.e. puffing up, sneezing, a clicking sound when they breathe, diorriah , etc etc it all helps with finding what was behind it :)

Good luck
Katie