@PharmaZ,
There is algae on the top of the rockwool cubes but otherwise no algae, all healthy looking white roots.
Do you think it could be clone degradation/senescence? I have no idea of the clones history, they could be 15 generations old. The reason I wonder is I have two clones from the same plant. They are completely symmetrical in the NFT tray and under the light, the environment is as far as I can tell identical so if something is wrong for one plant the other should surely be effected similarly.
like