Water changes should be fine. 5 gallons a week on a 14 gallon tank? That would be 30% or a little over which seems like a lot based on your light bioload. 2 gallon/week would still be 8/month which is more than 50% each month, and plenty for a tank with just a few corals that need calcium. I wonder if your nitrate and phosphate are really low from the water changes and the torch is losing tissue from lack of food. Have you had nitrate and phosphate tested?
and just a FYI. Shouldn’t dose anything without testing first