I had been noticing performance issues with my skimmer lately. It just wasn't pulling out the dark nasty skimmate I have grown accustomed to over the past few years. Today I went downstairs and checked out the tank.... The skimmer was full of pretty large bubbles and no foam. I thought to myself, WTH? I just cleaned this thing and let it run in a bucket with a water/vinegar mixture. The pump works perfect and the skimmer itself is clean as a whistle. Then it occurred to me. In order to get the tiny bubble and foam mixture, it has to be pulling in AIR along with the water. DUH.
So I took apart the pump intake assembly and tried to blow through it. Nothing...
I grabbed a pipe cleaner and tried to stick it through the hole, no go. It took several tries to push through the calcium build up. Man, there was a ton in there. I pushed through and put it all back together.
Now she is skimming like day 1. Well, a lot better than day 1, since it has been broken in for some time now.
Moral of the story: When you clean your skimmer, be sure to clean all of it.