Can you explain how hydantoins work on chlorine to me? Just so I understand.

I tested my hypothesis again today - this morning at 730 am numbers were TC by OTO of appromimately 5 with FC of 4 and CC 1; at noon TC by OTO was closer to 3 with FC of 3 and CC of 1 by DPD-FAS so I decided to add approximately 1/2 gal 12.5% bleach - and retested one hour later at 1 pm. ( 10k gallon above ground pool)

Here are the results: TC by OTO = approximately 5
FC 5; CC now 6


Clearly the new bleach is being routed to CC despite no one using the pool - just as I have seen over the past 2 weeks with each addition of fresh chlorine - and evidenced by little rise in the free chlorine. And also I think it seems out of the norm that my chlorine levels are so stable - for days even - without any new bleach or stabilizer at all. Something is stabilizing it and I imagine trying to maintain a pool in this state would be impossible.

I did find one other person on a different pool site who was experiencing similar problems - as you all had mentioned before - but he stopped posting and so there is no follow up. I wonder if he or reesie used the CDX system? there has got to be a group of people who used this system and are now trying to convert - so I am sure this problem has to be coming up - although if everyone only listened to the pool store, no one would be testing CC and people would be using their pools once they were clear not aware of the problem.

Now that we know about the hydantoins, does that change all of your minds about the benefit of the percarbonate and was it copper sulfate additions? This is an above ground pool - how risky is a drain refill? would it have to be fully drained or could a foot of water remain? would that leave enough hydantoin circulating in the fresh water to continue to cause problems?

I would rather pay someone to come and oversee the drain and refill to make sure it was done in the best way - (any of you want to fly up to good old massachusetts?????? ) But it sounds like there still is a risk of damaging the pool? I need to find someone good and someone who will understand why we are doing this. That will not be an easy task!

In the meantime - the good news is that I don't have to keep checking the pool that often because the chlorine is nice and stable! But I'm not sure if it is worth it to keep adding bleach - it seems like nothing is better from 2 weeks ago. I will wait to hear back from you all. aciam