I'm not the expert here, but I can tell you that the first question that anyone will ask is "How are you testing your water? Pool store, guess strips, OTO - red phenol, DPD, or FAS-DPD? All here recommend that you do the basic tests yourself, partly because MANY pool stores do NOT give accurate results. The Taylor K2006 or the K2006-C are the test kits always recommended. They are the same except that the C kit reagents are 2 ounce rather than .75 ounce.

This link tells about the test kits (typically not available locally) and provides links to order from Amazon. http://pool9.net/testkits

I'll also tell you that with CYA at 40-50 ppm, you want to ALWAYS keep a minimum of 5 ppm free chlorine. This link explains why. http://pool9.net/cl-cya/

Do you know the make and rating of your pump?
Do you you fill from city water or a well?
Is the water clear, cloudy, greenish, blueish, swampy?

I bet someone who can answer your stain questions will respond soon, and they'll be better able to help you if you answer the above questions.

Good luck!

Pappy