Blooms are falling off

[Cleveland]

I’m a Beginner. I purchase a Phalaenopsis orchid from a local grocery store. I put the orchid in a south. facing window (placed on the window ledge) and made sure it had indirect light. I watered it once a week using distilled water. Temperature is 68 day time and 64 at night. After 2-3 weeks it dropped all its blooms and pods. However, the leaves look healthy. In fact it’s growing a new leaf. So I purchased a second phlebotomists and it’s now doing the same thing. What am I doing wrong? The medium in the pot is bark. I need some help.