You may need to (do this carefully!) to either boil it or somehow pour very-hot water all over it; then submerge or wash in/with cold water. Let it cool and rinse/scrub any solid remains in/with tap water; then rinse in treated tap water and place it back in your tank.
Or you could let it be while you go through the fishless cycle, it might disappear once the tank fulfill the
nitrogen cycle. It is not unusual to experience bacterial bloom, alge bloom, both or even a bacterial bloom that resembles algae bloom while going in fishless cycle.
Involuntarily, but neglectfully, I introduced ick to my Rainbowfish tank a few days ago through a piece of driftwood that allegedly came from a healthy source. Obviously it wasn't.
Pepe
Santo Domingo