Corallife 300 cone skimmer

[RDNanoGuy]

Have you dosed anything in the tank? Many chemicals used for treating problems like algae cause skimmers to go haywire. So do many reef glues and epoxies. Try running some carbon in filter bag for a day or two, then try to adjust your skimmer again.

[scuba ken]

Your 100% right, but unfortunately I haven't dosed anything through the tank for at least a month, 6 weeks.
The skimmer works well for 2 or 3 days, then goes crazy, and just pushes water through itself.

[viperfish]

Take a close look at the amount of buildup on the neck of the cup. Some skimmers will build up a very thick coating on the skimmer neck and after a few day a large chunk will fall back into the skimmer and the skimmer overflows because of the large amount of DOC's hitting it at once. If this is the case you just have to clean the collection cup more often.