Preparing your rockwool cubes before you start using them in your hydroponic system is very important. The reason you want to prepare your rockwool cubes is simple - the pH of rockwool is unstable and will cause problems without proper preparation.
Unprepared rockwool will cause your pH to fluctuate greatly, which can cause your plants to become locked out from nutrients, this will eventually kill them. Extreme pH fluctuations over a short period can kill your plants in a matter of hours.
Preparing your rockwool cubes is very simple! This short guide will explain how to prepare your rockwool cubes.
The first step is to give your rockwool cubes a thorough rinse with clean water. I recommend using distilled water for this. Once your cubes are rinsed, soak them overnight in a water solution with a pH balance of 4.5.
In the morning, remove the rockwool cubes from the water and measure the pH of the water solution that you soaked your rockwool in. The pH should be around 5.5. If it is between 5.5 - 7.0, then repeat the soaking process.
If the runoff measures 7.0 or higher, then soak the cubes in a phosphoric acid solution with a pH of 4.0 for 30 minutes, then rinse / flush thoroughly. This will help neutralize the alkalinity and stabilize the rockwool. Re-soak the rockwool in water with a pH of 5.5 and measure the pH of the water solution after soaking for 8 to 12 hours.
Once your rockwool is prepared, add it to your hydroponic system and run it for a few days without any plants. Keep a close eye on the pH level, you want to keep it around 5.5 - 6.0. Once the pH is stable, you're ready to start growing!