Buffering your alum treatment is a safeguard against drastic pH change. I learned the hard way. If you add the "right" amount of aluminum sulfate, pH won't be affected. But, add just a little too much, and pH will plummet. Aglime won't be as responsive to a mistake as hydrated lime. If you choose to use alum, keep an accurate pH measuring device, and proceed with caution. Have hydrated lime on hand, in case you boo-boo. Read the pH before you start, and as you go.
When applying alum, watch the water. Clumps of dirt will form as you reach the "right" amount. It's okay to stop applying, as you reach saturation. Watch the water. It will tell you
