ASM G1 skimmer issues

Hi everyone. Just looking for an opinion, I picked up a used ASM G1 skimmer (older version with G500 pump). Was a good deal, body is in perfect condition, no cracks or leaks. However I am just not getting good skimmate. I have the riser tube above the neck of the skimmer and it just isnt producing after a couple weeks. If the riser is up higher I start getting skim but its very light green and watery. So I have set it so bubbles come just up to the inside neck of the skimmer cup. Thus when I remove the cup the bubble head is almost or just slightly over flowing the skimmer. I also notice that the bubbles seem to be large rather than a fine foamy type. I tightened up the bulkhead going into the skimmer, completely cleaned the pump, venturi and connections. Only thing of note was a couple of prongs on the impeller were slightly bent. Should I get a new pump or impeller? I was planning to do the gate valve mod but being disappointed in production so far I thought I would try other things first. Thoughts or opinions greatly appreciated!