Mine always pulled out black colored crud. I had the water level in the skimmer about 1" above the red ring.
I should also mention that I turned it off a while back for 2 reasons.
1. I was tired of re-adjusting it every day.
2. I was moving everything into a new tank, so I didn't have to have it running.
I really liked this skimmer at first, but after having my new Reef Devil that never has to be adjusted, my opinion of the super skimmers has changed. They need constatnt adjusting and are more trouble than they are worth.
You can set it like I had mine set, but I pormise you will have to adjust it at least every other day to keep it skimming properly.