Ca Chl usually is a whitish looking liquid. Green sounds like anti-freeze BUT I'd be cautious. If it was used stuff, chances are it diluted with water. Water + iron = oxidation (rust). Some fellas use windshield wiper fluid as well but that stuff too contains water nowadays. The valve stem area usually the first place to exhibit oxidation (rust). The liquid ballast is contained inside the tube. When the tube leaks, it gets onto the steel and will begin to oxidize. When you press the valve stem, any liquid will escape and get on the area around it. If you want to check air pressure or inflate tire, rotate the wheel around so the valve stem is at the 12 O'Clock position. I use Beet Juice, trade name Rim Guard ® ™. It is guaranteed non-corrosive. I've been using it since the mid 90's. Also advisable to invest in new tubes when switching ballast compounds. I.E. if you have Ca Chl and want to dispose of it and replace with Rim Guard, get new tubes so no contamination is presented. Wash out inside of rims with a good cleaning. If you are really concerned, the use of wheel weights is an option and no liquid at all. Take a sample of the liquid to a trusty AG Tire dealer and they can tell you exactly what it is. The 2000 is a great tractor so might be well worth getting the rims inspected now before they get rotted out from whatever is in there.