I have performed a number of freshwater dips and would recommend it, along with regular garlic treatments and copper (see below):
1) Perform a freshwater dip to remove all external parasites and most of ich
a) Get a 5 gallon bucket of RO
water, put a heater, airstone, raise the temperature to your main tank temperature and raise the PH to match the main tank with marine buffer (buffer max from API) and run your airstone.
b) Net fish and place in 5 gallon bucket for 4-5 minutes - watching extremely carefully for fish to stress out. At the first sign of heavy breathing or stressing out remove the fish and place in quarantine tank or main tank. All of my fish made the whole 5 minutes. If the fish seems to be doing really well, go an extra minute or two.
2) Place fish in 10 gallon quarantine tank and treat with copper medication per the directions - usually 10-14 days
3) Use concentrated garlic in main tank 1 drop per gallon or follow directions to add to their food daily - this helps prevent many parasites and improves their slime coats.
Let me know if you need any other advice.:hat: