Hey,
@Minion s1 - Hate seeing that.
From the looks of your plant, the stem is damping off.
Are any of the others doing that? Basil has a pretty tender
stem. Is there any way to make the plug drier around the
top? Looks like the plant is trying hard to cope.
I have never heard of that being a problem growing
hydroponically. Perhaps the sponge is too wet around
the stem. Growing in an AeroGarden, I have never seen
that. Maybe someone with more hydro chops can give a
better answer.