Repeated dipping can be stressful. Do you have pics to confirm POX ?
One thing truly works although peroxide, iodine, etc have worked for some. . . . . Furan-2.
Simple process:
1. Mix a fresh batch of saltwater. It is preferable to use freshly mixed saltwater as apposed to water from your tank to ensure anything that may be causing the ailment in the first place isn't included in treatment. Take special care to match the temperature, salinity and PH of the aquarium that the colony is kept in during treatment.
2. Take one cup of fresh saltwater and mix one packet of Furan 2. Use a container small enough to insure that the colony is completely submerged. Larger colonies will require more water for the treatment so keep the ration of water : Furan 2 the same. Keep an additional container of untreated saltmix on hand for rinsing.
3. Place your colony in the mix and let soak for 15-20 minutes. Do not exceed 30 minutes.
4. After the dip, rinse the colony in the second container of untreated saltwater and place back into the aquarium (again a separate quarantine tank is suggested).
5. Let the colony rest for 24 hours and repeat steps 1-4 for two more days.
After the third treatment it is advised to let the colony rest for 1 week and monitor its condition. If you feel that the condition hasn't improved, another round of treatments should continue