Peat moss pellets, they wash off very clean and easy once I'm ready to transplant them. Nothing is held close to the root ball to cause nutrient miss-balance or Ph problems I control everything, no guessing, no other issues. I just learned my lesson many years ago.

<Hint> You may want to cover the top of your Rockwool or Alga will start to grow. </Hint>

That's just me I'm sure you will be fine.