Hydor 600 skimmer - Help!

[slough shark]

I`ve got a hydor 600 skimmer its about 3 months old and for the first while it was skimming great. Lately I`ve noticed the production drop like crazy. Now its so bad that I can barely get the foam into the neck of the canister. Its still foaming a lot and i cleaned all the lines, all valves are wide open. Does anyone have any tricks to make the foam climb into the neck
Any help would be much appreciated.