Tried the second batch of kraut and it turned out okay. I left it in for four weeks this time and unfortunately there was some mold situation during the last week. Apparently you can scratch it off or remove that layer and, sure enough, the kraut was totally fine. However, the thing stank up the whole apartment and it looked and smelled gnarly.
I’m not sure what the problem was; a lot of the liquid evaporated very quickly for some reason and adding some water probably caused the problem.
It’s still too salty for my taste, so I’ll reduce the amount again for the next batch.