We get a lot of call with people complaining about dross on their cuts (I had one yesterday) and also that their tungsten tip looks a little weird at the end or the TIGs is not welding right.
A lot of times it's bad gas (we call it that) or moisture.
Here's a video, from welding tips and tricks, on making an inline water filter that can be used on your TIG argon tank or plasma cutter.
You can buy them as well, like I do, but I might make one as I can build it bigger and make it last longer.
http://www.weldingtipsandtricks.com/...gas-dryer.html