Possible sickness/Fungus?

First of all, please sparen comments about this wird setup.

But does someone have a good guess on what might be affecting my wasabi there ?

I had a lot of stems die because they would turn black over night, "shrink" in that area and break off.

I guess it might be some Fungus since it affects all plants who share the same water reservoir. Therefore, I normally remove all affected stems to kind of hinder a possible reproduction of spores or so.