How can I disinfect an aquarium decoration, to add to a different tank?
The ornament is probobly safe as is. you could rinse it in hot water. Bleach is very safe when used properly. You have to make a 10 part bleach solution, never soak for more then 15 minutes. Then rins in hot water. the only thing left will be chlorene, it will disapear when the item dries in 24-48 hours, and or rinse it in some water with a dechlorinating product. Go the the bleach websight if you are still unshure.
You can use a 10% bleach solution and then soak the ornament in some Seachem Prime if you're concerned.
Chlorine bleach breaks down to water and table salt. Don't worry about it.
Use a bottle of isopropyl alcohol. It'll disinfect the object and evaporate cleanly. Alternatively, submerge the item in boiling water for several minutes, provided it's made of a material that withstand the heat, to sterilize it.