Alum to clear a pond

[PondFin@ic]

I've been researching using Aluminum sulfate to clear ponds and I think I'm going to try it. With feeding this year and little rain my pond isn't as clear as it was in past years both from planktonic algae and suspended clay from runoff in the nearby fields. Here's an interesting article
http://www.minneapolisparks.org/default.asp?PageID=832

I found the dosage is 60lbs per acre foot for moderate. For my pond that works out to 220lbs. It will lower the PH so my plan is to add about 40% hydrated lime immediately after spraying a slurry of the alum mixed with water over the ponds surface to bring the PH back up.

The other option was gypsum. Gypsum was more readily available but was going to be more costly and a more work than I wanted to do moving literally a ton of the stuff.

Here's my calculations. Anybody have any thoughts on ups and down of doing this?

11' Max depth
7.333333 Avg depth
21780 Sq. Ft. (1/2 acre)
159720 Cu. Ft. water
159.72
12 Rate Gypsum per 1000 cu. ft.
1916.64 Pounds Gypsum needed
0.1 Cost Gypsum per pound
$191.66 Cost to treat with Gypsum
Results in 1 to 4 weeks
1916.64 Total pounds to distrubute


3.666666 Acre feet
60 Lbs Alum per acre foot
220 Pounds Alum needed
0.65 Cost Alum per pound
143 Cost Alum
40% Ratio Hydrated lime to balance PH
88 Pounds Hydrated lime
0.1 Cost lime per pound
8.8 Cost Lime
$151.80 Total Cost to treat with alum
Results in a few hours to a week
231 Total pounds to distrubute