The higher the Alkalinity, the more Alum you have to add. A local pond guy told me I need to add acre feet x alkalinity in terms of lbs of alum to be in the ballpark of what I needed. I ended up using about 260 lbs per acre foot ballpark.. So he was pretty close. I would think 260 lbs per acre foot is considered high in your experience?
I didn't add the lime because I have no fish.
