The "clear blisters" sometimes end up being flukes. First step would be to do a freshwater dip to either confirm or eliminate flukes as the problem. Here's a thread on how to do a FW dip:
Freshwater Dip What It Treats – Provides temporary relief for a wide range of diseases: 1) Marine Velvet Disease (Amyloodinium ocellatum) 2) Brooklynella hostilis 3) Uronema marinum 4) Flukes (Monogeneans) 5) Black Ich (Turbellarians) Can be used to confirm the presence of Flukes (see video...