I think why everyone is on the fence is because Hydroton doesn't hold water (or enough anyway)

Everything looks good with everything, 18/6 is another fence issue. It allows the plant a regular Calvin cycle
Personally, I think the dark reactions are just as important as light ones.

As to constant drip I am not to sure. Rockwool watering is usually 15min every 4ish hours though.
I might say you need more intervals. Is it really aerated? Root rot in your situation could be drainage. No standing water in your pots?