membership updated; thread moved to algae section. -ben
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Aylad pretty much answered your questioned, but you haven't posted back, so I-m not sure if you were put off by the answer, or didn't understand how to follow through. On the chance that you didn't know how to follow through (rather than simply rejecting the answer), I'll post two links that explain WHY you need to do what she said, and HOW -- testing-wise -- you can do so:
http://poolsolutions.com/gd/best-gue...ine-chart.html explains the WHY;
http://www.poolforum.com/pf2/showthread.php?14994 explains what you need to test, or the HOW.