I have read that it's important to soak these cubes in water adjusted to a PH of 5.0. Thus conditioning them prior to planting. Is this information correct and if so just how do the commercial growers soak a 1,000 or so at a time?

First, the reason we recommend "conditioning" the GRODAN products is to remove a lime stone residue in the block. The lime stone, which is pH 8, dissolves easily with pH adjusted water. Once the lime stone is flushed out, the GRODAN product is pH neutral. 

Due to the difference in equipment and especially in stock tank size, the recommendation for commercial grower and for hobby use varies.

Hobby: We recommend soaking and flushing the products, as you typically use a recirculation system. Having the dissolved lime circulating around in a small tank would make it harder to maintain the proper pH in the system. Also an important aspect of using stone wool is that the product most be fully wetted before use. By recommending the conditioning we are sure the product is fully wetted before use.

Commercial growers will wet up the GRODAN slabs typically 24 hours before use. When they wet up the blocks varies a little from grower to grower. However, most growers in North America 'water to waste' (as in non-recirculating).This means the lime stone is flushed out as soon as the irrigation system starts. Those growers with a recirculation system have computer controlled automated fertilizer injection. This means the computer will automatically compensate for any undesirable E.C. or pH fluctuation.

Important Note: GRODAN does not tolerate lower that pH 5.0 - it starts to dissolve. So to be on the safe side, I would suggest you soak in pH 5.5. This will dissolve the lime fast. After an hour or so, you simply water from the top with your balanced nutrient. For each "HUGO" block you need to top water at least one gallon of water, as the block holds near that amount of water. Now your block is perfect for planting and you can transfer it to your system.

You can use a garden hose to soak your blocks with. However the tap water is often very close to pH 8, so it is best to soak the block overnight.

Thank you for using GRODAN!