Since sulfamic acid combines with chlorine to form both N-chlorosulfamic and N-dichlorosulfamic acids, the effectiveness of the chlorine is reduced and the sanitizing properties are not well known.
The minimum recommended ORP for a pool is 650 mV.
So, an ORP of 629 is a little bit low.
The recommended dose of sulfamic acid is 10 lb per 10,000 gallons, which adds about 120 ppm sulfamic acid.
If we assume that the equilibrium for sulfamic acid is roughly equivalent to cyanuric acid, then the 7.5% ratio would indicate a TC of about 9 ppm for good sanitation.
Below is a quote from one study.
Approximately 1.000 mg/1 chlorine in the form of dichlorsulfamate would have to be established to achieve a 99 percent kill of E. coli in 1 min in the pH 7-8 range.
However, the study does not really go into equilibrium, which I think is a mistake.
They really need to know the ratio of sulfamic acid to chlorine and not just a combined chlorine reading.
In any case, one should be aware of the lowered effectiveness of the chlorine as far as providing sanitation.
For a low use residential pool, I think that the risk is low.
For a high use commercial pool I would probably drain and refill or SLAM.
Since you are getting an FC of 1 ppm, that is a good sign.
If you raise the TC to 9 ppm and if you can get the ORP to 650 mV, then that would be a good sign of sanitation.
Passing the OCLT is a good sign that there is nothing growing.
Having zero algae is also a good sign of adequate sanitizer since algae generally takes more chlorine to control than bacteria.
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