4th Gen HELP with Psyducks on path to Celestic!

[IMTHEONEKILLINU]

I need help! The Psyducks that block the path to Celestic that have headaches, are giving me a headache! What do I need to do to get them to move?

I have the Prima guide which is useless. I think that I need a potion or something, and it may have to do with the girl at the Grand Hotel who is missing her Suite Key. I used the Dowsing Machine on the beach which is what Prima says to do, and two gray dots appear. When I line up the crosshairs over the dots, I can't pick anything up. Help and is this what I even need to be doing?

Thanks in advance.

 

[Ichida]

Talk to Cynthia near Lake Valor after chasing the Galactic member in front of the Great Marsh.

 

[IMTHEONEKILLINU]

Cool thanks! I talked to her, but didn't chase the Grunt! I'll try that. THANKS!

Outstanding! That worked like a charm! Thanks again. I was talking to the wrong girl.