The different concentrations (0.5~8.0 mmol/L) of sodium bicarbonate solutions were prepared in six aquaria (200mm× 400mm×300mm), and then potassium nitrate(1.0mg/L), potassium dihydrogen phosphate(0.2mg/L) and plankton filtered by 25# net were added. The experimental carbonate waters were tested once every 24 hours and the nutrient solutions were timely supplemented. The changes in pH value were tested under the condition of photosynthesis. The results showed that pH value was less than 11 in single carbonate waters, and pH value was varied from 9.23 to 10.66 in summer. The changes in pH value were also tested in the carbonate waters supplemented with different concentrations of calcium chloride or magnesium chloride. The results showed that pH value was correlated with the concentrations of carbonate, Ca2+and Mg2+and illumination in carbonate waters. The inhibition of pH value was in-creased with increase in the concentrations of Ca2+under a certain concentration of carbonate. Likewise, the inhibition of pH value was increased with increase in the concentrations of carbonate under a certain concentration of Ca2+, but the soda water was formed when the concentration of Ca2+was significantly lower than the concentration of carbonate in natural waters. The inhibition of pH value was increased with increase in the concentrations of Mg2+. However, the inhibition of pH value only occurred in carbonate waters with pH value of over 9.63 at Mg2+concentration of 10-2 mol/L. In the 0.5 mol/L carbonate waters, the corresponding pH value was increased from 9.90 to 10.33 when the illumination was increased from 2290(at 6:00) to 54200(at 9:00). The pH value was shown to increase with increase in illumination at weak illumination. When the illumination was changed from 47500 at 12:00 to 88700 at 15:00, howev-er, pH value was changed from 10.39 to 10.44 in carbonate waters. The findings indicated no significant correlation between illumina-tion and pH value at strong illumination.%在6组200mm×400mm×300mm的玻璃缸中配制0.5~8.0mmol/L碳酸氢钠浓度梯度的溶液，加入硝酸钾（以氮计1.0mg/L）、磷酸二氢钾（以磷计0.2mg/L）和用25生物网过滤养殖池塘的浮游植物样，之后每24h检测一次水体营养盐并及时补充，在光合作用条件下检测pH变化。结果表明：单一的碳酸盐水体pH小于11，夏季水体pH在9.23~10.66之间；在碳酸盐水体中加入不同浓度的氯化钙和氯化镁检测pH变化，结果表明，水体pH与碳酸盐、Ca2+、Mg2+含量及光照度相关。碳酸盐浓度一定时，Ca2+含量增加，抑制pH的能力增强。Ca2+含量一定时，碳酸盐含量增加抑制pH的能力增强，但在自然水体中Ca2+含量明显低于碳酸盐含量时易形成苏打水；Mg2+浓度增加，抑制pH的能力增强，当Mg2+浓度为10-2mol/L时，Mg2+只对pH大于9.63水体有抑制作用；在0.5mol/L碳酸盐水体中，光照度由6：00的2290（Lux）增加到9：00时的54200（Lux）时，pH由9.90增至10.33，pH增加明显。12：00至15：00时光照度变化范围为47500~88700（Lux），水体pH变化在10.39~10.44之间，变化不明显。
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