A 200-year-old Chinese mansion in Bangkok’s heart isn’t an obvious place for a scuba school, but in a city relentlessly demolishing its architectural heritage the business is helping preserve the historic home. Dive instructor Poosak Posayachinda’s family has owned the traditional teak-walled So Heng Tai for eight generations, but it lives on thanks largely to his decision to convert it into a scuba academy. The survival of the building, originally built as a home and office for the family business trading birds’ nests with China, is a rare success story in a city that harbours little sentimen…