You do need to invest in a good test kit. Definitely worth the money. While you are fighting this, test at least 2 and 3 is better times per day and each time, add enough bleach to get back up to 20. Try to sustain the high reading and not let it yo-yo up and down.

I still don't think your numbers are right, though. I have never seen a CC reading of 10. Retest and repost.

You aren't filling from a well, are you?