Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Bass Dying all of a sudden

My bet is that the herbicide spray combined with no aeration and high water temps created an O2 crash, and without aeration it is taking the pond a long time to recover. I saw it in a friends pond that I have been after him to get aeration in for the past 6-7 years. It finally bit him in the butt. 3' TGC, 20+" HSB, 4#-5# LMB and 8"-10" BG dead 3-10+ days after spraying about 1/4 of the pond for coontail/algae. He has been guessing at water temp too, and finally broke out the thermometer to actually check water temps.

I checked the O2, and in the afternoon when the O2 typically is highest, he had 5-6 mg/l, but go down 3 feet and it was in the 4mg/l range and below 4 feet it dropped to the 3mg/l range. 6 foot was below 1 mg/l. Surface water temp was in the low 80's. He first noticed the fish stop feeding, then a few days later started seeing dead fish. The O2 would vary according to water temp, and a suppressed feeding response was a good indicator of dangerously low O2 levels.

We threw in a bottom diffusion aeration system with 2 single disc diffusers with a 1/4 hp compressor in the pond, but that still isn't enough for a 2 ac pond with a max depth of 12'. A larger compressor can't be used, the power supply can't support it. We tried with a 1/4 hp and 3/4 hp rotary vane compressor and the air output was less than with the 1/4 hp rocking piston compressor. That will be changed for next year, and a 3/4 hp rotary vane compressor will be used with 2 more airstations.

It took 3-4 weeks for the O2 in the pond to come back up to where the fish are feeding now, and in part I think that is due to cooler water temps (by 5-6 degrees).

Multiple fish don't die at the same time from starvation or low food availability - it was an O2 crash. The herbicide used had no effect on the fish kill other than killing the plants that then decomposed and the bacteria that was decomposing the plants sucked up the O2 which in turn caused the fish kill.