Go ahead and shock it. Use the chart at this link:> http://pool9.net/cl-cya/
Keep the chlorine at shock level until you meet 3 criteria:
1) You lose no more than 1ppm of FC from sundown one evening to within one hour of sunrise the next morning
2) You have no higher than 0.5ppm of CC
3) The water is clear.
Run your pump 24/7 while you are trying to clear the pool, cleaning your filter as needed.
Go ahead and run the CH (calcium hardness) test one time. Although vinyl pools don't need calcium, sometimes if it is high it can cause problems. Also, did you run the CC test when you did your FC test?
By the way, what are you using as your source of chlorine? Your CYA is pretty low. Are you having trouble making it through a hot sunny day with a chlorine reading?
Hope this helps.
(Hint: Use a 10mL sample instead of a 25mL one. It will make your chlorine testing reagents last longer. You'll multiply the drop count by 0.5 instead of 0.2.)
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