Liming calculator
Use agricultural limestone only. Never put hydrated lime or quick lime in a pond with fish. Spread it over the whole bottom, or the shallow margins if the pond is full, in fall or winter. A bottom soil test from an extension lab beats this table. The effect lasts 3 to 5 years; recheck alkalinity each spring.
Method and sources
Alkalinity under 10 ppm: 2 tons (sandy), 3 (loam), 4 (clay)
10 to 20 ppm: 1, 2, 3 tons
20 to 50 ppm: 0.5, 1, 1 tons, only if you plan to fertilize
Table rates are for pure calcium carbonate (100 percent CCE) and follow SRAC publication 4100, Liming Ponds for Aquaculture, and Mississippi State Extension publication 1428, Managing Mississippi Farm Ponds and Small Lakes. The bag or quarry sheet gives the neutralizing value of the lime you can buy; the rate is scaled up for anything under 100 percent. Finer grind acts faster, so ask for material that passes a 60 mesh screen.
Alkalinity under 20 ppm is the gate: fertilizer does nothing until lime brings it up, and fish production stays low. Between 20 and 50 ppm the pond grows fish without lime, so liming is only worth it if you fertilize. At 50 ppm and over no lime is needed.
Practitioner discussion: Pond Boss forum thread Fertilization of ponds.