How to prep and treat Rockwool for horticulture use:
1. Place Rockwool in the seed flat or other container to soak. You may want to wear gloves when handling dry Rockwool to avoid skin irritation.
2. Add water with a pH of no lower than 5.5 and no higher than 6.5 for 30 minutes. To reach a pH of 5.5-6.5 you can either use a commercial pH lowering product or lemon juice. For precise results, I recommend testing the pH of the water as you add the pH lowering substance.
I used a ph kit I have for soil which worked just fine. Turns out our well water was within the recommended range without any adjustments. You can use the general recipe of juice of ½ lemon to 1 gallon of water to lower 1 pH point.
3. After soaking for 30 minutes, drain water and rinse with more water with 5.5-6.5 pH. It’s important not to squeeze the rockwool at this point.