Welcome to this forum and hope you will enjoy the discussion here.
In regard to your question, I think storage closet should be ok but not fish pond. We need earth luck inside our home and it is inauspicious to dig something or disturb the internal ground. Furthermore having a stairs above a water pond make the stair look like a bridge. Imagine you need to cross a bridge everyday and a bridge symbolize something that is unstable and dangerous. Your life will be very stressful.