Our water makes us cough when the water fall is running

Our 22000 gal SWG outdoor pool has started to make everyone cough when the water feature (slide and waterfall) is running.  I have taken the water to my local store to analyze and for the most part (Chlorine was actually slightly low) everything is in balance.  The things that I have recently done:

Changed the cartridge filters (Pleatco brand), added PhosFree, added 6 lbs CYA (only read 25 in my analysis so still low).

It is only when the water feature runs or vaporizes the pool water.  I have wondered if it may be related to the construction of the feature.  Our pool is new but it has been dragging on for 3 summers now.  The pool guy has added new Epoxy on the slide to make it smooth but not sure if anything else has been added.

Everyone I have asked is baffled.  Any thoughts?