THE APPLICATION OF 1120 KILOGRAMS OF BASIC SLAG PER HECTARE (HA) RAISED THE CONCENTRATIONS OF CALCIUM, MAGNESIUM, CARBONATES, AND BICARBONATES, DEPRESSED CARBON DIOXIDE TENSION, AND ELEVATED PH, BUT SIGNIFICANT TREATMENT EFFECTS IN THE PHOTIC ZONE WERE SOMETIMES MASKED BY THE DIEL EFFECTS OF PHOTOSYNTHESIS AND RESPIRATION. IN DEEPER WATERS BELOW THE PHOTIC ZONE, BASIC SLAG AND LIMESTONE CLEARLY ELEVATED PH AND CONCENTRATIONS OF CARBONATE AND BICARBONATE, AND INITIALLY DEPRESSED FREE CARBON DIOXIDE. LIMESTONE AND BASIC SLAG AND DISSIMILAR EFFECTS. NEITHER TREATMENT RAISED TOTAL HARDNESS TO THE LEVEL OF HARD WATERS; THEIR ONLY SIGNIFICANT EFFECT ON POND BOTTOM SOIL WAS A SLIGHT INCREASE IN PH. THE BIOMASS OF SESTON AND BENTHOS AND BLUEGILL PRODUCTION WERE UNAFFECTED BY LIMING. DURING 6.5 MONTHS, THE EXPERIMENTAL PONDS PRODUCED 140 TO 290 KG OF BLUEGILLS PER HA.