Quote Originally Posted by rayh78
Update
I just checked it with the test strips and everything is now reading the highest level. What would cause the CYA to go up on its own?
I am guessing it is time to drain and replace at least 1/2 the water?
Test strips just aren't accurate enough, especially if there is a problem. If possible, please take a water sample to pool store and have them test for free chlorine, total chlorine, combined chlorine, CYA, alk, pH, hardness. Until then, we really can't give any reasonable advice. We would also need to know the type of pool, and its volume.

Most probably, chlorine went to high to nothing because some bug is growing in water. Increased chlorine should do the trick, running filter 24/7 is critical also. However, without accurate water reading, you can only guess. And guessing can get you in more trouble.

CaryB