high dissolved organics and bacterials will make it foam a lot. It makes it hard to estimate how long the break in period will be. If you "calibrate it" the way Roger suggests, it zeroes it out. and makes a common until the break in is done and then you can really dial in the skimmer. My 9001 took a long time in my current tank, it took no time in the first tank I put it in and the the 9004 I have took only days.
Once its a fairly consistent fluid gong into the cup then you can start tweaking
Once its a fairly consistent fluid gong into the cup then you can start tweaking