I hope your skimmer is okay, and you just need to build biofilm back up on that part for the cup like saratj1 said. If not, I have been using a reef octopus hob
skimmer. bh-100 is the model and it's excellent. About 30% fill up so far in the cup. Had the skimmer less than 1 week. Hopefully I don't run in to the same problem when I clean my cup.