That's a pretty expensive kit and you're right it did get pretty good reviews. (I wasn't familiar with it, so I looked it up.) The downside to it, though, is that it is a DPD kit and will not test high chlorine readings like the K-2006 will. Also, from what I could tell, there is not a CC (combined chlorine) test with that one which is also an important piece of information to have when you are fighting algae problems. Some reviews also suggested that the CYA test gives low readings and the calcium hardness test is not too accurate. Maybe ChemGeek or Waterbear will have information on this kit that they can share.

Hopefully, someone can help you figure out what those black marks are. Glad to have you here on the forum with us!