Peat moss pellets work just fine.
If you are going to grow in Hydroponics they wash off the plant with easy and not get any dirt or anything in your reservoir.
You can then plant just the seeding in the grow rocks and not have to worry about Rockwool retaining water and soaking the root ball, or holding nutrients around the root ball.
It will save you Ph problems as well as the chance for toxic salt buildup & nutrient imbalance around the root ball due to excessive water build up.

Rockwool is the #1 grow medium sold at grow stores (so they say). Itâ??s just not my favorite thing to use for the reasons I stated above.