All freshwater meds work with cold as well as tropicals.
You need to find out why the fish has finrot before you start to treat and checking water quality should be your first step.
Find out what the ammonia, nitrite, nitrate and ph levels are and working towards good water quality is always the first step.
Next is the tank and filtration big enough? Goldies are big waste producers for their size so you need 10 gallons minimum per fish and a filter with lots of media in it.
How much is changed per week and is there a gravel vac used?
Once you have got great water quality, you can use aquarium salt to stop any fungal infection at 1 level teaspoon per gallon twice 12 hours apart.
When doing water changes, remember what you take out and replace it with the salt. It takes many weeks for the fins to start growing back in but the hardest part is getting it to stop because if it reaches the body then little can be done.
In a gallon of water add 3 teaspoons of salt and dip the tail only into the solution for a few seconds then return to the main tank. You will need to do this every day to stop the rot.
Any remedy for finrot will work but only if the water quality is great.
