Hi, Ann, and welcome to the Pool Forum! With a CYA of 170, your chlorine readings are way too low and you may be on the verge of an algae bloom. Take a look at the Best Guess Chlorine Chart in my signature below. With that high of a CYA reading, your chlorine always stay between 8-15ppm. I'd advise you to shock your pool up to 25ppm and try and hold it there until you can go from sundown one evening to within two hours of sunrise the next day without losing more than 1ppm of chlorine and the water is clear. Then, keep the chlorine high for one additional day and then you can let it drift down but never let it get below 8ppm.

You're going to have to buy a kit that can measure high chlorine readings. All the kits you'll be able to get locally will only go to 5. The Taylor K2006 or 2006c (see test kit link below) will measure up to around 50 I think. It is only available online, so go ahead and order it so it will get here sooner rather than later.

In your pool, each gallon (4 quarts) of plain, unscented 6% household bleach will add about 5.5ppm of chlorine and each quart will add about 1.5. Use this as a reference to help you figure out how much bleach to add each time you test.

What kind of kit are you currently using? I suspect that you may have an HTH 6-Way kit. If so, you can force it to read higher than 5ppm with a dilution method described here: Testing Without a Good Kit

Also, please fill in your pool's information into our pool chart as it makes it easier for someone here to help you.

Pool Chart Entry Form

Hope this helps!