Was reading this thread:http://www.troublefreepool.com/calci...ns-t68511.html and need a bit of clarification not really answered in pool school extended-test-kit-directions-t25081.html
When I do the CH test, when I reach the point of first color change, the indicator appears to "clump" into miniscule flakes, which appear violet or purple. It then takes about the same number of drops to turn them to a obvious blue. I am assuming that this is the "metals interference" indication. Looks like I will have to order the appropriate test modules from Dave to find out how much is in the fill and pool water, and possibly start using a sequestrant.
Side note for chem geek: According to a conversation with a local water company employee, they keep our domestic water at a relatively high pH -- above 8.4 -- with TA target around 100 ppm (his words) "to help protect the cast iron mains". Does this sound reasonable?
They also use what he described as mono- and tri- chloramines in puck form as a sanitizer. However, some of this seems to differ from their published water report, seen here: http://www.amwater.com/ccr/mx.pdf The actual report starts at page 4 of the PDF.