I would have set up a quarantine tank for the goldfish instead, but in any case, do a 10% daily, not a 30% water change. The larger change should be at the beginning and the end of treatment. Add Aquarium Bacteria at the final water change as well.
After the final water change, and adding fresh carbon back to the filter, wait 24 hours, minimum, before putting snails, catfish, and plants back. So....they can go back, assuming the goldfish is well....on Monday, Feb 12.
Date published: 2018-02-07