Smimmer quitting just from clean tank? My skimmer has stopped skimming. It still makes bubbles. But they don't make it past the neck. Only other time I noticed it quitting was when the diatom filter was running which pulls everything fine out of the water. I cleaned the pump in vinegar for 2 1/2 hours. No skim. Over a week . Ita a 120 with two 5" fish. It had a small grouper before which increased the bio load and feeding.