The store name seems to be much more important than the grand couplet.
More water indicates illusion and impermanence, and the yin nature hides misfortune.
The combination of cloud and water has no ancient charm. Unless Yun makes it clear. The industry you are in is related to ancient Chinese culture. The word "water and cloud" is unlucky and superficial.
Mingguan is the rename of the ancient fortune-telling and calligraphy shop by later generations. The Feng Shui destiny prediction theory was born when King Wen asked for divination. The name should reflect its mystery and sacredness as it goes back to ancient times.
Would the shop owner consider changing the name of the shop to a more subtle name such as "Yibun Juntu" or "Xuanji Pavilion"?