Healthy UK native species tank, but pond snails always die (nerites thrive tho)

[Martinspuddle]

The only thing I was going suggest was maybe using drip acclimation.

Edit: If this one does survive and then goes on to thrive in your aquarium, I wouldn't add any more. Being asexual, you soon built a colony.

[plankton]

If you have a pond for when they get to big then that's ok.
I was worried about the potential growth factor.
I haven't seen that site before, so they must breed bullheads in captivity, which will help with conservation.
I don't know why the filtration would be a factor against the pond...do you have filtration in the pond? How "similar" is the water?