Since I was responsible for a sizable kill here at work last Friday I figure I'd let others know where I went wrong. Realize that I am in a much different system(flow through) than most of you folks here and so treatments are quick and highly dosed. In fact I have a 10 minute retention time in any one tank.
So what happened: (this is the report I turned in)
Week prior: Heavy rain caused yo-yo effect on temperatures of spring. Water also became cloudy on several occasions. Temp range 13.6-15.9 over the course of hours several times as most extreme storms passed over. Oxygen dropped below 60% on Thursday when water warmed, so oxygen was added as well as additional flow from pond water source.
4:00pm- Notice colonies of what appears to be a fungus in irregular shapes on about 60 % of fish in the B-line. Appetite of fish seemed to be reduced, some food on bottom. Applied ¼ teaspoon of potassium permanganate to each head tank and 1 tablespoon to the main head tank.
8:00am- No deaths from treatment. Little to no improvement on situation. Decided to try 35% h202 at a rate of 1.5 gallons per raceway, given in head. Also added 4 gallons (4 gallons at time with 10 minutes between doses) to head tank after all raceways were treated.
9:00am- A few fish start to look stressed. Added 50lbs of salt per tank to length of tank to attempt to calm them.
9:30am- Fish in the 4b look extremely stress, colors of fish changing. Took DO in QZ in the bottom of B and A and found both in the 140s%. Tried to drain water faster by turning on geotube pump and pulling standpipe. This had no effect.
11:00am- majority of fish in tank 4b are dead.
12:00pm- Deaths taper off, some fish come back from the death on bottom of tank 4b.
Bottom line: treatment was too long, at too high of rate for the last raceway while the upper tanks were fine. Furthermore, fish with disease were too comprised for this treatment. The A line had little to no death in any tank except for the last unit.
This was my fault, not a system fault. The serial raceways just added to the potential that I would make a mistake.
The system is actually quite simple, and works fairly well. It would be exponentially better if I could cover the spring, but that would be way too expensive.
Total loss was 959 lbs and 586 fish. Still less than 10%.