I’m fighting a light case of ich on another fish and setting up a qt tank today
This fish is in the same display tank as the one with
Cryptocaryon irritans (Marine Ich)?
Marine Ich isn't selective. It will infest any ornamental marine fish. All fishes will need to be treated in the hospital tank following the
14-day copper treatment (you'll need another tank for observation) or the 'usual'
30-day copper treatment.
As to the display tank:
Studies have shown that about 45 days of the display tank going fishless are reliable if you can raise the DT temperature to 27C (80.6F) and there are
no dormant Marine Ich in the DT and DT system. If you have a FOWLR DT, raise temp to 30C (86F) for 15 days, again assuming there are
no dormant Marine Ich in the DT or DT system.
Marine Ich can lay dormant in low oxygen (anaerobic) areas and able to survive longer than the above times. To avoid this, you want to reduce/eliminate areas of low oxygen. These areas include:
1. Thick substrates -- need to be 'disturbed.'
2. Rock sitting on substrate can hide dormant Marine Ich;
3. Canister filters -- need to be broken down; and
4. Rock crevices can hide dormant Marine Ich.
Use high circulation and 'blast' under rocks and into rock crevices -- as much as any corals you have can take. If there is any part of the system which you feel may have low oxygen areas, find and eliminate them.
After removing/eliminating low oxygen areas,
then begin the times noted above.
If raising the temperature above 78F is not an option, then go 75 days after removing/eliminating low oxygen areas. Keep in mind the
Pitfalls to going Fishless.
As to those spots on the Clownfish, they are most likely bacterial infections
unless they look fuzzy (having filaments rising off the body). A closeup video under white light would be more helpful.