Pond Boss Forums INTRO Questions & Observations crazy idea with alum

ok...infrequent poster but avid reader. I have learned a lot...most of what I have done is wrong...as one of the gurus said its the third, fourth year when you really have to adjust. So learned the hard way about shallow water aeration for winter...but..by measuring all the dead fish learned I was doing something right...lmb 18 - 24 inches.
So the question of the day...probably not that different..from t many others..we get inundated with heavy rains..never before... with excess runoff coming into pond from overflow pipe. Have FA issues, seemingly under control with cutrine plus and se clear...however now have huge plankton bloom...not seen before. can still see 12 - 18 inches down but the question is...does it make sense to put an onion bag of alum in front of the over flow pipe to minimize
phosphorus. Did use some alum a few years back, monitoring ph etc.
This would not be ph monitored as the overflow comes in. Thoughts?
Doing my darndest to answer all the obvious questions ahead of time.
Again, cant thank everyone enough for all the great info

Forgot to mention...NOT for water clarity but an attempt to capture excess phosphorous
From primary source of runoff.

Well I do just that but with calcium carbonate. We can get rock lime in big chunks and I let all the inflow water wash over these as it enters our pond over the waterfall. The thoughts is to help change the phosphates in the run off to calcium phosphate.

I am not sure the water has enough time to react but the calcite rocks are soft and are dissolving.

The only years we have alga problems that we can't cure with dye is the years our wheat field is close to the pond and it just happens the wind is the wrong way then the wheat is taken off. The chaff blows into the pond and the alga explodes in two days.

Cheers Don.