Goldfish fry.

Question
Each year I take a dozen or so fry out of the pond and  leave them for a year in a filtered aquarium then return them to the pond in summer. This year I did the same using pond water and tap water with aqua safe added and an air blower. They grew to a quater inch and I added a filter. Within 24 hours they were all dead. They looked perfect, fins up and  a test on the water showed no nitrites at all. I took out the dead, did a large water change and put a few more in this time with no filter, put in three fry, two died the next morning and the largest was gulping water so he is now back in the pond. I am at a loss as to why.
The tank is 4 ft and I only fed them liquid fry food ( not live) I want to try again should I have baged and floated them, I didnt last year. Any advice would be useful if they stay in the pond they will be eaten by the larger fish.
Thanks
Mercia

Answer
Mercia,
I am not to up on goldfish fry but I would imagine they are like others. They are very delicate and should be handled with care. I am thinking that when you put them in the tank, it was not cycled? When you added the filter, it then started to cycle. You tested for nitrites but did you test for ammonia? Ammonia will show up before nitrites because if the ammonia is left in the tank it turns in to nitrites. If the pond is well planted, the fry will be able to hide in them until they are big enough to not be eaten. Was the water they were going into the same temperature as the water they were coming out of? Even a 2 degree difference and be detrimental to the fry. Some fry will die because there is something wrong with them. I know I haven't been that great of help but I hope what I have said will help.