recirculating systems using rockwool allows rockwool to build up toxic levels of certain nutrients. That is why Porfessional commercial growers drip to waste. If you apply fresah nutrient solution...It is said that it will control the toxidity levels of the rockwool, because with the fresh solution the nutrient levels are balanced.

I prefer to use hydroton in drip systems, due to the inert nature of the expanded clay.

I only use rockwool for cloning or seed starting, and the blocks do well in dwc, because you are not washing nutes over/thru the rockwool causing the ph to fluctuate. So unless you are dripping to waste; you should look into changing your medium. later gotta go