The TF-100 is a nearly exact copy of the PS234 I developed, and as such, is much more accurate than the computer testing.
To answer your questions:
1. Your chlorine levels are not unsafe for swimming, but they were unsafe for swimSUITS. (High chlorine + low CYA will kill swimwear quickly; high chlorine + high CYA does not usually).
One quick rule of thumb: swimwear at both the extreme low end, and at the high end (> $100), is not very chlorine resistant at all. Low end suits (<$30) can be worn at the beach or in un-chlorinated water; high end suits are really just made for show, not swimming. Of course, in the in-between range, some suits are very sensitive and some are not.
2. BUT, with the low CYA, chlorine levels will drop rapidly in full sun.
3. Or not. Sustain literature reports that their "Sustain Summer Shield Chlorine" produces residuals that test as "combined chlorine" but aren't. My guess is that they ARE combined chlorine, but not the common ones. Having to investigate this -- the Sustain program may be using old-tech: sulfamic acid as a sun shield, and chloro-sulfamic acid compounds as 'chlorine reserve' and algae inhibitors.
Here's what PPG has to say:
http://www.ppg.com/chemicals/askjoep...s/080_oto.aspx
You might want to look and see if this patent number is on the bottle:
http://www.google.com/patents/US6471974
I'll have to get back to you on that.
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