These pieces of drift wood are labeled for use in aquariums and fish bowls. Do not use pieces of wood that are not labeled for use in aquariums. Something that I can contribute is the fact that even though you state not to use bleach , I find that it is an effective and safe way to sterilize my picks of the creek , when done correctly. I live in Philadelphia. I m not sure if you ever visited, but it's not the cleanest of cities.
Some parts have nice parts though, with creeks running through.
I go often with my backpack and gather nice river rocks and gravel. I then fill a two-gallon bucket with hot water and about five tablespoons of bleach. I let it sit for about five minutes or so and rinse well. Then I refill with more hot water and add about two tablespoons of the water conditioner you mentioned. I let that sit for a few hours and then rinse again.