I do know of lots of people who use Rockwool, Iā??m just not one of them anymore. Your idea should work just fine, keep the light away from the Rockwool and alga should not be a problem. Rockwool is probably the #2 grow medium in the world. Just look around and you will see who uses it and how many problems they have too. There are more problem grows then there are success stories in the past 4 years with Rockwool on all the forums.

The only correct way to use Rockwool is to presoak it like you said.

Grow rocks can experience toxic salt build up yes. If you flush between vegetation and flower cycle you donā??t have that problem. Grow rocks only hold water in very small, small amounts. That by itā??s self helps to keep the nutrient build up down. Flushing for preventive measures is always a good practice and eliminates that problem.

Rockwool by design retains water and that can be a receipt for problems of over watering and a number of other nutrient imbalances.

If you get the system dialed in right Rockwool can grow fast too. Itā??s just not my cup of tea thatā??s all.

Hell Iā??ll use Rockwool over Miracle Grow any day.