Pond Boss Forums INTRO Questions & Observations Tilapia al swimming on surface. Why?

Yesterday, I did a water exchange like I normally do while I vacuumed the bottom of my 1500 gallon pond. Following that most of my young tilapia (2nd and 3rd generation) started hovering on the surface while gulping for air while swimming backward in unison. Total fish in pond including goldfish is perhaps 200.

Fish piping at the surface is a sign of a dissolved oxygen sag. Are you aerating?

They used to swim in schools on the surface in my pond.

Low O2. When you did the water exchange, was it well water or was it water that had O2 in it? My guess is water was put into the tank/pond that had little or no O2 and it dropped the O2 level in the pond by half.

+1 on low dissolved oxygen.

In my old aquarium keeping days, a 10% water change was considered safe so long as the frequency was often enough. The frequency depends on the bio load in the aquarium. If I let the tank get off schedule, I would often perform a 20% water change without issue. I was not pushing the limits of biomass to gallons of water.

How much water was exchanged? How often is this performed? How much biomass in the tank? What was the difference in water temp between tank water and new water? What's the average length of fish?