It may or may not be fusarium, but even if it is not it is a similar pathogen. Pics would be helpful. It may also be phylloera or hemp canker as well, both have become more and more common in recent years. All of the above will cause symptoms like you describe. A lab test would be needed to properly ID it however.
I've dealt with it successfully in soil but I am not sure quite how you would deal with in in a RDWC system. In soil properly made aerated compost tea and predatory nematodes helped keep it in check. Myco Stop may work but it is only effective against certain pathogens, it is not a cure-all. Not sure about
Greencure, have not tried that one myself.
Serenade probably would not have any effect (it is more for mildew), but I'm not sure, maybe it would attack the fusarium so you might try it anyway. Once infected, the plants are pretty fucked though, you can never really get rid of it, best case scenario is you can keep the plants alive and healthy long enough to finish flowering.
Generally the most effective way to deal w/ this sort of issue is to ensure proper drainage and aeration in your soil. These sort of pests usually only get going in unhealthy soils with poor drainage and aeration. Once infected, the soil must be given a rest of several years or be disposed of completely. Now how that related to RDWC I'm not sure, but hopefully that helps.
Also you need to treat your plants like the have the plague. That means full quarantine with your grow. Anything in the room MUST be sterilized. Any tools leaving the site MUST be sterilized. After working in the room, change your clothes and take a shower, ESPECIALLY if you are going to another grow. It is nasty shit to deal with, I wish you luck!