So I have read chem Geek’s last post several times to make sure I am understanding it – and wanted to present a data point from last Thursday that might shed some light on what you were thinking in terms of equilibrium of DMH and chlorine release – I have not ever done the FC CC tests on a single sample waiting 10 or 20 minutes in between tests – BUT I do have some data from multiple tests close in time after adding bleach.

Last wed I dumped a lot of bleach into the pool desperately trying to get my FC to 12-15 which was the level recommended to me on this thread – I had no more titrating reagent and was relying on “cheap” kits – the OTO for TC and DPD for FC by color matching. I could never get to 12-15 despite all the bleach I was adding – but in retrospect I now can see why. So once I got my new reagent in the mail I decided to test at multiple points after adding bleach to see what was happening to the bleach in the pool – this is when I first noted that all the bleach was combining with something to increase my CC incredibly high but only raising the FC a minimal amount.

So, last Thursday at 1pm I tested with my new reagents and got a FC =8 and CC=16

I added 1 and ½ gallons of 12.5 % bleach at 1:20pm – which should have raised the chlorine level by approximately 15 -18?? Is that right?

I tested 20 minutes later ( at 1:40) FC=11.5 ( slight inc) and CC=35 (huge increase)

I retested (a new pool sample) 20 minutes later again ( 2pm) FC=15 (now higher) and CC=25 (now lower)

After that the testing shows both numbers slowly decreasing.

I present this in case it helps to clarify your thought process – that in fact the new bleach being added seems to be primarily binding to something (the DMH presumably) right away and testing out as CC – and then slowly dissociates to increase free chlorine levels and decrease CC but only to a point. I don’t know what is governing that dissociation equilibrium. Nor is there any real consistency to the numbers – some days the CC can be high without even adding any new bleach.

I haven’t done any other testing so closely in time to adding bleach so have no other data points to present.

What I do know is that it is nearly impossible to achieve high levels of FC in this pool without pouring in huge amounts of chlorine thus causing the CC to skyrocket – and the CC levels seem to stay in the lower range when there is less free chlorine measured.

SO I guess the question is can we break down the hydantoins in any effective way to change the chemistry of the pool so it works properly. I am curious to see if madwil gets any information from his buddy at the water plant - that might give us some insight into whether anything we do could actually breakdown these substances. And whether I really need to seriously consider a drain and refill.

Then if we decide to try the percarbonate – I suppose I will need everyone’s consensus on how to do it – 1 pound or 2 per 1000gal – acid or no acid. I’m not sure I was clear on the final recommendation. Perhaps that’s because none of you are either ☺

I feel like I am back in my organic chemistry class in college – and let me tell you all – I did not like organic chemistry!!!! It is like a nightmare that has come to haunt me all these years later……..My husband just shakes his head at me when he ventures down to the basement to see me with all my bottles and reagents. It is kind of comical. If I wasn’t so upset about all of this, I’d really have to laugh at it. Maybe after this is all done I will. Thank you for all of your help. aciam