yeah salt
Using salt (aquarium, kosher or pickling) is more natural and kinder to the fish. If its what you want to go with then you will need to add the salt to the correct solution and then turn the heat up to 80f.
Salt the tank by adding 1 level teaspoon per gallon for a 1% solution. 12 hours later do the same to get a 2% solution, and the same again 12 hours after that to get a 3% solution.
You must remove any live plants and keep this solution for a few days after the last spots go and then do small normal water changes to slowly get the water back to fresh again.
What you need to do whilst salting, is to do gravel vacs every 3 days of 50% to try and get rid of any cysts in the gravel.
When replacing the water remember how much you took out as you will have to replace the salt taken out. For instance, if you take out 10 gallons add 30 level teaspoons to the water.
If you need to top up due to evaporation then dont add salt.
If after all that you still want to use the meds you have then make sure you have lots of aeration and you keep the lights on the tank off, and raise the temperature to 80 as well.
Hope that helped
Are there no other fish in the tank apart from the goldies? no loaches?