Pond Boss Forums GENERAL QUESTIONS Muddy water Fish Kill after Treatment

HI Guys,

I had a large fish kill after treating my chocolate milk pond. I applied 400#s of Alum, and 200#s of hydrated lime on my acre pond. The weather here the past week has been brutally hot ( possible not enough oxygen?). My pond was stocked with HSB,CC,HBG, and unfortunately black crappie (they were already in the pond). There are a few hundred 3-4 inch black crappie lining the shores 10 catfish and I have only spotted 7 HSB (turtles might have thought they tasted the best?). The pond looks like a swimming pool now which is great, I am just not sure I have any fish left to enjoy it.

So here are the questions for the experts
Was it the lack of aeration that killed the fish?
My PH was 7.6 before treating, not sure if that was the cause?
What should I do moving forward? Kill the rest of the pond? try to save what is left? ( if any)

Pond like I mentioned is about an acre with an average depth of 4ft and the deepest portion being 9ft deep.

I appreciate your help as always,

Wait a few days. Test alkalinity. Survey (fish ,seine survey if possible and look at) the lake to see what is left.

I thought crushed lime was favored over hydrated lime? I use hydrated lime to sterilize and kill fish in my hatchery ponds.

I realize the alum and lime kind of cancel each other out but...

Should I try to remove the dead fish or let mother nature handle it?

Camo, my best guess, from treating many ponds with alum, is that you applied the Hydrated lime first, and did not get the alum applied fast enough to limit the rapid pH climb of the hydrated lime. The other scenario in applying Alum/Lime, is not applying it evenly and ensuring a good mix of the 2 slurries to offset one another..ie pockets of very acidic alum treated water and pockets of highly caustic Hydrated lime treated water. This makes pH shock potentials VERY high with nowhere for fish to escape "bad" water.

Did you see fish launching themselves out of the water during or after the treatment? See any fish piping?

Crappie and HSB are very fragile in these high water temperatures, so I'm not surprised you lost several, but the dead CC make me think there was a fast, wide, pH swing that shocked the fish and killed them.

There is really nothing you can do now but wait a couple weeks for the pH to stabilize from the chemical treatment. You could go ahead and lower the water level as much as possible, add a few hundred more pounds of Hydrated Lime and kill it, if wanted also.

Cecil, Hydrated Lime (Calcium Hydroxide) should be used with Alum to offset/balance the Alum's acidity, immediately. Ag Lime Calcium/Magnesium Carbonate/ is slow acting and for long term pH buffering/raising. Ag Lime will not react nearly fast enough with the Alum to prevent a pH drop/fish kill.

Makes sense Rex.

In my area our Ph is so high (8.4 to 8.5) and alkalinity so high (about 350 mg/l in my ponds) it isn't even necessary to add anything to counteract a PH drop after adding alum as it doesn't happen. When I did aquaponics I had a hell of a time dropping the ph and many times it would bounce back up.

I only use hydrated lime to kill off remaining fish in standing water in a drained pond. It literally burns up any frogs, tadpoles, or fish that get in the way. Pretty mean stuff!

Thanks Rainman, I applied the lime last after the 4 hours it took me to spread the alum slurry all around my pond ( wow that was a lot of work). I didn't see any fish piping, and I thought I did a pretty good job of spreading it evenly( spraying with a garden hose using my trash pump). I had to treat this pond two years ago using alum, and didn't have any issues, however last time I did not use the lime?

camo...The alum will turn the water acidic relatively slowly. Depending on how many acre feet of water (I'm guessing about 2-2.5), the alum probably lowered your pH as much as 2 points, causing a moderate shock. Adding the Hydrated Lime, your pH would have jumped back up to the starting pH, within minutes of the H lime being applied. That is a pretty harsh shock, and easily could have been lethal.

To help avoid others causing a shock kill, alternate applying 2 50# bags of Alum, followed by 1 50# bag of Hydrated Lime sprayed in the pond, in a proportion to the total pounds and total surface area. This will help reduce the pH shock, plus leaves untreated, and pH balanced areas for fish to retreat to during application.