How long does an alum treatment last?
The original treatment to remove colloidal clay is permanent. The Alum also removes any Phosphorus that is present during the treatment from the water, permanently, as well.
Colloidal clay is attracted to the Alum/Lime like metal fines are to a magnet. Also like a magnet, only a finite amount of metal fines can be bound up within the magnetic field.
The highly positively charged ion's of the Aluminum Sulfate and Hydrated Lime that settle out in the bottom will act like a magnet to attract a considerably large amount of any incoming colloidal clay.
As to "how long" the treatment will last....That depends! After the initial treatment to clear the water, sunlight penetration will allow submerged plants, phytoplankton, and other aspects of the ecosystem to grow and thrive, helping to filter or ionically remove future incoming colloidal clay from the water. If large amounts of colloidal clay remain exposed and able to get flushed into the pond after a treatment, it can overwhelm everything and cloud the pond indefinitely again.
