OK. So 2 questions:
1)CC is already at 0.5. Do I even need to SLAM? (water is clear NOT Crystal; minor algae dust during brush)
2) IF YES, then I add 581 oz to achieve a Shock FC of 20 ppm, I am done if 1) water crystal and CC is 0.5 or less; AND 2) OCLT is less than 1ppm. so if I SLAM tonight to achieve 20 ppm; a 19ppm the next morning would be an acceptable OCLT. Correct?
I am not sure if I am reading the SLAM directions correctly or not. Thanks.
You can't stop the SLAM until your pool is crystal clear. You must pass all 3 criteria before you finish and none of the criteria is an "OR".
Once your water is crystal clear, you can do the OCLT.
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Oh, not sure if the was already mentioned, but some algaecides add metals, so you need to stay away from them.
It is best to stick with polyquat 60% and verify that it doesn't contain copper or other metals. Around here, we recommend only using algaecide under a few situations like closing your pool and when you purposefully need to bring your FC to 0, like during an ascorbic acid treatment.