Disease ID

[dragonfish]

Need help with a possible disease or other cause. Major die off in pond. Changes made right before are, large addition of new fish, additional filter, more rock and sand, a new food.
Symptoms observed:Lethargy, lack of appetite, cloudiness of eyes. Occasional surface breathing.
Losses are convicts, jag, dempseys, tinfoils, severums, GT's, nics, uro.
Survivors without any signs are:Silver dollars, lyonsi, pleco.
Water parameters are and have been, Ammonia 0, Nitrite 0, Nitrate <10.
Any suggestions would be appreciated.

 

[uselessmidget]

How big is this pond? its possible there over crowded and theres a lack of oxygen in the water, you can try an airstone.

 

[Lupin]

Your pond sounded overstocked to me. Oxygen depletion is possible. What test kit are you using?

 

[dragonfish]

How big is this pond? its possible there over crowded and theres a lack of oxygen in the water, you can try an airstone.

600 gallon. Have two pumps on it. one at 1400 gph for filter and one at 200 gph for circulation. Lots of current and surface agitation.

Your pond sounded overstocked to me. Oxygen depletion is possible. What test kit are you using?

API master test kit. Not out of date or off. Other than oscar largest fish is 6 inches. Compared to alot of tanks on here and one that I had running, not even close to overstocked.