Most growers would agree that it is a good idea to clean the hydroton before using and then again after each use if you decide to reuse it. New hydroton will have dust all over it so it is definitely a good idea to wash all of this crud off.

My favorite way to clean hydroton is to use a 5 gallon bucket with a bunch of holes drilled in the bottom. Fill the bucket with hydroton and run hot water through it. You can also use a Florakleen solution to help kill off any unwanted bacteria/growth from the clay pebbles.

Another more complicated but very thorough method is to use two or three 5 gallon buckets of dirty hydroton letting them soak for a couple of days in a trash can filled with water and a bottle of Florakleen to break down the salts and such that are absorbed into the hydroton. Then I tumble them in fresh water in a portable cement mixer I bought from Home Depot that I used for another home project. I usually have to run them through several times but it does the trick for me. Also I add some bleach to the next to last rinse to kinda disinfect them.

Another alternative if you prefer not to use any type of disinfectant is to boil them or let them soak in boiling water. Then you can bake them at like 200 degrees for 10-20 minutes to sterilize.