I did 80% water cahnge in my tank 3 weeks ago,skimmer has not been skimming since.anything wrong ? changed air stone(wood)2x to check if that was problem but still nothing.skimmer is hang on (amiricle).
You took out 80% of the dissolved organics. Water changes and skimmers do a lot of the same thing, IMO, but skimmers can stretch out the amount of time between WC. Give your skimmer time, although you should be noticing some crap starting to come up. What kind of hang on skimmer?
Those skimmers are not very powerful and it's positioning in the tank(height) will affect how it works. Plus what qwiksilver said may also be contributing to the lack of scum collected.