Preparing Rockwool Before Planting

Soak new rockwool in full-strength CropSalt nutrient solution adjusted to pH 5.5 with RunClean before you plant. For a recirculating soak, use pH 6.0 and keep adjusting it back to 6.0 until it stops climbing. New rockwool carries alkalinity from production (we call it a coating), and the acidic nutrient soak neutralizes it. A plain-water soak doesn't.

Condition new, unplanted rockwool

1. Mix full-strength nutrient solution from our feed charts. Dissolve the A first, then the B.
2. Static soak: bring the complete solution to pH 5.5 with RunClean. Use plenty of solution and wet every cube, block or slab all the way through. A small bath can lose its acidity before the whole batch is conditioned.
3. Recirculating soak: hold pH 6.0 and keep adjusting back to 6.0 until the pH stops climbing. Mix each adjustment through the bath before you read it.
4. Let the excess drain per the substrate maker's instructions before planting. Don't leave blocks sitting in the drained solution.

We've used about 30 minutes for a small, thoroughly wetted batch and longer soaks for big batches. Complete wetting, enough solution and a pH that holds matter more than the clock.

If your mix doesn't need pH down, add RunClean at 0.2–0.4 mL per gallon for scale prevention and recheck the pH. More on rates in what RunClean does.

Running feed through the drippers isn't a soak. If slab tops are still dry the next day, the rockwool wasn't conditioned.

After planting, feed normally

The 5.5 soak is for conditioning, not a feed pH. Once plants are in, run the normal program and compare feed with the last 10% of runoff. Rockwool takes the same nutrient program as coco: 4.6 g Veg A + 3.1 g Veg B per gallon through flower day 21, then 5.1 g Bloom A + 2.6 g Bloom B until Cake. Only the watering changes.

Seeds started in rockwool use the Veg seedling ratio. Clone plugs and cuttings use the propagation mixes in rooting clones with CropSalt. Keep that nutrient choice separate from conditioning the rockwool.

Already planted in unconditioned rockwool

Don't put rooted plants through the new-block soak. First confirm the high runoff pH is from rockwool that was only soaked in plain water, not underfeeding or a dosing error. Then:

1. Mix the complete A+B at the highest strength on the label.
2. Adjust it to pH 5.6 with RunClean.
3. Feed with a decent amount of runoff. The goal is pH 5.8 in the last 10% of runoff with 5.6 going in.
4. Once you see that, go back to normal feeds.

This is a one-time correction for that starting problem, not a new routine feed pH.

Wet the whole block

Small shots through one dripper can leave part of a block or slab dry while the runoff looks fine. If water runs down one channel, move the outlet or spread it across more of the block, then check wetting again. If a block stays saturated, lengthen the interval. If it dries too far, bring the next feed forward.

If growth stalls, compare feed with last-10% runoff pH and EC; see how to test runoff. Low runoff pH from buildup gets the tap-water flush in why runoff pH is lower than feed pH.