The less algae (phytoplankton) in the water, the more P will be suspended in the water for the alum to work on (less tied up in the algae). Lets see what Rex says, I'm more inclined to use 300#/150# per Ac/Ft water.....
Depending on the weather trend (is a warm front coming or a cold front?) I would hit it with Cutrine Plus in the low 50°F range if there was a warming trend coming.
That's kinda why I want to hear back from Rex. The first year I did 350#/150# and it was sufficient but I had strong flow-through about a month later and the nutrients have never really been utilized since, so it's been a green factory situation for a good part of last 2 yrs.
Send him a PM, and if you don't hear back soon, let me know, I have his phone number.
