I've never gotten a good answer for the phenomenon. Small blocks always have a ph stability problem. Once I put plants onto slabs the ph stays pretty level, but they're also getting watered periodically by a drip system rather than by hand. I thought it might be a result of the moisture level...
Perhaps some of the more experienced growers could answer this one:
If I have rockwool slabs in dutch trays that drain into a well aerated reservoir (two 6 inch air stones in a 20 gal reservoir), is there any reason why I can't run the drip system continuously as a sort of hybrid between NFT...