I am having trouble with my pond im not sure if i need more ar pumps plz help?

i have been having trouble with my pond for two days the ponds 400 gallon i have a good filter that waterfalls back into the pond and another waterfall and 1 small air pump for the past two days i have had 2 fish ill 1 koi on its side just floating on the top and 1 upside down floating but the rest are ok i have put some pond salt in and some anti bacterial i haven't tested my pond water because i don't have a tester i have had this pond for 1 year and had no problems dose any 1 think that there is not enough air in the water