Pond Boss Forums GENERAL QUESTIONS Water chemistry Alum choices

Alum is a loosely defined chemical group, with different formulations depending on source and differing weight of Aluminum for a given weight of the alum. So does it really matter which you use? Most floc treatment recipes are trying to remove excess Phosphorus and talk about the amount of aluminum required per ppm of Phosphorus, but usually don’t specify which “formula” for Alum they are using. Are some types easier/safer to use? Are some more easily dissolved/slurried? Cheaper per weight of Aluminum?

The reading I've done has all been about a finely granulated aluminum sulfate (food grade). Copy of a test report I had run in May.

Here's page 2 of the report. I don't have it saved as a jpeg so I can upload it to my knowledge.

Total phosphorus in this sample is 0.0 ppm which would place this water into the oligotrophic range
(low phosphorus) for surface waters in the U.S.
Clearing test results
This pond has higher concentrations (>50 ppm) of hardness (70 ppm) and alkalinity (74 ppm), and
they are relatively balanced in a 1:1 ratio, so agricultural limestone (calcium carbonate) and gypsum
(calcium sulfate) will not be highly effective clearing agents for this water chemistry. The only viable
option to clear this water based on the chemistry present is alum (aluminum sulfate). A moderate
clearing effect was obtained at 60 lbs of aluminum sulfate per acre foot of water while a significant
clearing effect was obtained at 75 lbs of aluminum sulfate per acre foot. Because this water has an
alkalinity of greater than 50 ppm, the addition of hydrated lime (calcium hydroxide) is not required,
but it is still suggested to add 0.43 lbs of hydrated lime per pound of aluminum sulfate added to
prevent lowering of alkalinity and rapid pH changes that could harm any fish present. Hydrated lime
can be mixed in with the aluminum sulfate and added at the same time (makes a putty like paste or
slurry) or added intermittently between adding bags of aluminum sulfate. For more information on
pond clearing chemicals, rates, and application methods, please see our publication at
https://fisheries.tamu.edu/files/2021/09/clearing-muddy-ponds.pdf.

I’m probably a little to picky about this but I’ve seen alum described as potassium aluminum sulphate, ammonium aluminum sulphate, di-aluminum sulphate, aluminum sulphate, aluminum sulphate hydrate, dehydrated aluminum sulphate. All of these have different amounts of aluminum ions per pound of material. Most web sites or blog posts ignore these differences and just refer to pounds of alum. Most of the rest use these terms interchangeably. Is the chemistry all that forgiving that it doesn’t really matter which of these you use?