Think about this. When you clone a plant, you give them 0 nutes. Basically water and some rooting hormone. Once they root, then you can give them nutes. You can search through the forum here and find hundreds of people with little fried seedlings, because they were giving them nutrients. Your plants will grow fine without nutes for a couple weeks, or until the 3rd or 4th node. And no, people who do soil grows use promix and NOTHING else. The people who use soils like Miracle Gro run into trouble a lot of the times because there are already nutes in the soil. A proper soil grow is done with a nice soilless mix like promix or one of the many others. It has absolutely no nutrients in it, drains exceptionally well, and retains moisture very well. If your HTG guy, whoever it is, said that using soiless mix is like doing hydro, you need a new HTG guy, whatever an HTG guy is.