"Learning calligraphy by the pond"
The phrase in the pond is a quotation from "Book of the Later Han Dynasty,Biography of Zhang Zhi". According to Zeng Gong's "Records of the Ink Pool,"the calligraphy master Wang Xizhi also imitated Zhang Zhi.
尤好草書学崔杜之法
家之布帛必書而後練
臨池学書水為之黒
He was especially fond of cursive writingand learned the methods of Cui Yan and Du Du. He wrote characters on all the silk cloth in his house, then practiced to write the characters again and again. He learned calligraphy near a pond,so,the water turned to black.