CYA is stabilizer--it wouldn't be in the pool unless you added it, either by adding straight cyanuric acid, or using dichlor powder or trichlor pucks for chlorination. Its purpose is to protect your chlorine from the sun so that it remains in the pool to fight bacteria and viruses in the water. You need to know what your CYA level is, because that's going to determine the amount of chlorine you need to keep in your pool to keep the water clean. (see the best guess chlorine chart link in my sig for more info on this).

You should be able to call the county and ask for lab testing results of the water--they should be able to tell you whether or not it contains metals.

If your white thermometer string is green, then you have algae in the pool. Normally I would say go ahead and shock it, but first you need to know your CYA level and if there are any metals in your water.