Ich on goldfish in outdoor pond

[Lambside]

Fishnet-who knew? Anyway I have a lone goldfish in an outdoor pond of about 60litres. He had some yucky big white sores which I treated with Interpret goldfish disease aquarium treatment and the sores are now almost gone.
I also moved him into a different pond because I read that the treatment would kill off any other invertebrates and I didn't want all my snails sacrificed.
Now he looks to have Ich- tiny white spots on the outside covering of the gills. I'm reluctant to treat this pond because of all the snails in it. Ditto on the use of salt. Both ponds have several plants in them and would be difficult to empty and clean completely.
So can I treat it with just salt dips? If so how often and can anyone give me definitive amounts, after reading the internet I am befuddled with different amounts from 4tsp per gallon in a bucket to 30tsp per gallon in a tank.

Bump

Did you really mean 60 litres? Sounds a bit small for a pond and is way too small for a goldfish.

Well thanks for getting back to me. The only reason I think it's 60litres is that I looked up my buying history to find the capacity of the container.
That was to work out the dosing for medication.
Anyways I've picked out as many snails as I can find and dosed the pond again.
He's lived in that pond for seven years and seems happy. One day I may invest in a massive container for him.......

Barely visible non cooperating goldfish

Easiest way is to measure the diameter and the depth of water. Not sure from that picture if there’s a filter of some kind? How often do you carry out partial water changes? If it really is only 60 litres then it could easily be a water quality issue, an aquarium test kit would confirm. Goldfish should really be in 200 litres+