Holy crap I am shocked! It seemed like my ATB medium cone just wasn't really skimming like it used to, I really didn't think much of it because it still skimmed pretty well and my parameters have been excellent. So today I yanked the pump out and let it run, with air, in a bucket of vinegar/ro for about 45min. What a difference, I feel a little ashamed that I let it go that long. I clean the cup on a regular basis but hadn't dealt with the pump for far too long. Next stop will be the return pump, I am sure flow has slowed on that also. Again it hasn't caused any troubles but....
The only point to this thread is this, if your skimmer just doesn't seem to be what it used to be let that pump run in a bucket of vinegar water for awhile, you might be surprised.