Since you have a cya of 50, you can take your chlorine up to 6, and even higher if you want to. You can take it up to shock levels (which for you would be 15-20) if you do it slowly - you have to watch to see if any stain starts to form, if it does that means that you need more sequestering agent. Your ph is low at 6.8, you need to get it up to at least 7 with aerating. You may want to invest in a pool fountain since your fill water is high in alkalinity. Here is a link to what I am talking about.
http://www.intheswim.com/shopping/dept.aspx?deptid=1257&GCID=C14163x040&e5=Y&e6=swim ming-pool-fountains&keyword=swimming-pool-fountains&s_kwcid=swimming%20pool%20fountains|7349 26481

You can find other places that sell them if you just google pool fountain.
Hope this helps, and feel free to ask any other questions you have

Just another thought, what is your calcium level? What do you mean you can't get a reading? High calcium with high alkalinity can cause a lot of cloudiness, plus sometimes it causes stains too. It's just good to know where the stains are coming from.