My child was in a public pool when the staff put liquid chemical treatment in the filter. She said that she could not see her hand at arm’s length underwater because the water became so cloudy. Does this sound safe to you?
It is never a good idea to add any chemicals to the pool with swimmers in the water. Just how concerned you should be depends on what was added. For example, a dose of acid or base to adjust the pH could be very irritating to a swimmer while a dose of phosphate reducer to control algae would be much less harmful.