Have you added any chemicals like stress coat?
OR have you used any other chemical that is markted as a 'slime coat' replacment?
The reason is that your skimmer will go CRAZY in trying to remove this and will act exactly like you describe in filling the collection cup within seconds. If a tank is new and you have no DOC
's then your skimmer wont have anything to skim and it will take weeks to fill the collection cup so I feel that what your seeing is a result of some cheimcal that you might have added to the water.