Ich cysts typically last 3-28 days, then hatches and last for 24-36 hours - I would recomend that you vacuum your garvel thoroughly - though 220gal is a lot of gravel to vacuum. Personaly, i don't like to treat my display tank with any medications. I would recomend the use of malachite/formalin for treatment in your quarantine tank - and take some of your tank water and add to your quarintine tank - set up a
HOB/bio-wheel filter and wait at least 4 weeks - copper is difficult to use IMHO because it needs to be at a specific dosage continuously. I would also do 50% water changes on your primary tank every day for the first two weeks - and clean all filters and other equipment that has come in contact with your water - I know this is alot of work but better to be safe than sorry. I would recommend the use of a high wattage
UV Sterilizer - while i use a quarantine tank before i put new fish into a tank - wether good fortune or luck using the high uv sterilizer i haven't had any fish diseases.