I spent the better part of Saturday treating my tan colored pond with alum. Secchi disk reading went from 8" to 36" by the time I was done. With windy conditions the next day, I was dismayed to see only 24", but realized I could see the the downwind side was very clear and you could see a distinct line in the water between real clear and less so. Evidently the wind blew the best water over to that side, kind of turning the pond over. The day after that things seemed to be uniform and I could see the secchi disc spin at 40". Hopefully this lasts a long time!