I have a 2007 Sundance Optima...480 gallons, and I also use bromine. I have drained it 3 times over the past 8 months onto the same spot in my yard each time. It seems to have no impact on my lawn (doesn't seem to help - doesn't seem to hurt), but then again, I don't have a nicely manicured lawn...some grass, some weeds, some bare spots
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Others here have a lot more experience and knowledge than I do. Just thought I would post my experience...for what little that is worth.