Yes, the bubble type will tell you. If they are breaking at the top and it looks like boiling water, then it isn't picking up much organic material, yet. When the bubbles look stiff, almost soapy and don't pop immediately, they are carrying proteins on the surface of the bubbles. It increases the bubbles surface tension as proteins are generally a long chain molecule. Those are what you want to build up and overflow. Be cautious as setting the skimmer too high will result in just overflowing and dumping tank water. This concentration of the proteins can take a while and is what we call the skimmers break in period.