Added copper sulfate to a small pond... had significant blue gill kill off.. no effect on catfish. Ideas on how to counter the copper sulfate?

Copper Sulfate is a chemical used to kill algae. When algae is killed, the effects after include depletion of dissolved oxygen. If too much algae dies, too much oxygen is removed from the system essentially suffocating fish and causing a kill. It is best to treat the pond in sections and let it recover rather than treating the entire pond at once to limit oxygen depletion. In most cases of low oxygen the smaller fish are harmed the most (also catfish are brutes and are harmed less). There was probably just enough oxygen to keep the larger fish alive. Nothing can "counter" copper sulfate, it simply gets used up or dilutes to the point of ineffectiveness. So most likely the damage has been done and oxygen levels will proceed to rise to their normal points. Several other factors can cause low oxygen in small ponds, I recommend adding some kind of aeration to the pond. This can be expensive initially but serves as an insurance policy of sorts for your fish in any future low oxygen events.

I hate chemicals in my ponds...literally hate them. The copper will linger for a long, long time...and it may not have killed the catfish, but you can bet if they were tested for copper, it would be positive.

Yes, I may be fanatic, but if it were my pond and someone put copper sulfate in it (it wouldn't be me) I would drain it, dredge it and start over. I like my fish pure and my ponds without chemicals...but that's just me.

Thanks guys... pond is strictly for kids and grandkids to catch and release

Bottom line? I wouldn't do it.

In the ultra soft East Texas waters, copper sulfate can be directly toxic to many species of fish and invertebrates. To even THINK about using copper sulfate, you should have at least a total hardness and total alkalinity of 100 ppm. Even then you got all them other issues mentioned above, oxygen depletion, heavy metal residues, an such.

Lime first, then copper if you must.

Now most generally speakin' copper sulfate is fairly safe, I seen 'em putting it in drinkin' water down to the putrification, um, er, purification plant in Texas City. But...that copper ain't goin' nowheres one'st it done been put in the pond. It goes to the bottom and stays there, and can certainly build up over time. Add some lead shot from huntin' ducks an' doves, an' some arsenic from the natural ground runoff or the old cotton farm in your watershed (or even your water well), an' a tad of mercury along with a tad more of selenium from the local coal fired powerplant, along with all manner of aluminum, cadmium, barium, amongst others from the roadway, well you sorta get it, heavy metals is gonna be a part of your life even in the rural areas. Some believes its not good to keep adding more. I'm pretty much in that group with exceptions...

So to answer your question directly, nope ain't a darn thing you can do to "counter" the copper. HOWEVER, you got some dang good advice above with respect to adding an aeration system to your pond. One of two things that will most increase the productivity and maintain stability in your pond. The other is a feeding program.

There are other ways to control algal blooms. If you can get some tilapia, the right kind, specifically NOT the "legal" kind (which in fact most are not), they'll help a lot. What you want is "illegal" tilapia with the proper and complete paperwork stating they are indeed the "legal" type. The onus remains on the dealer to sell the right fish, not the purchaser to be an expert in the identification of over 100 species of tilappine fishes and countless hybrids. Besides, the TPWD has in the past, and publicly, misidentified a lot of tilappine fishes and even certified a blue tilapia (Oreochromis aureus) as a state record Rio Grande perch (aka "Texas Cichlid" Herichthys cyanoguttatus , formerly Cichlasoma cyanoguttatum) in the past. Only DNA can tell for sure. Remember that, it will be important if you get caught.

Planting the right kind of emergent vegetation around your shorelines might also help. Pickeral rush, iris, thalia, etc. can help keep nutrients away from algae and provide both habitat and landscape enhancements. Keeping lawn fertilizers out of the pond and watershed also helps a lot.

I have found that a well planned pro-active use of microbial adjutants to be very effective in preventing and even controlling algal blooms of all sorts. No poisons, no worries if the fish you got is legal or not, but a tad costly and demanding of planning and execution.

If poison you must, there are less innocuous ones. As a heavy metal, aluminum sulfate is less toxic, especially in soft water than copper sulfate. To 50 pounds of aluminum sulfate mix in 6 pounds of dry citric acid and spread on top with a scoop. Some poisons have limited long term toxicity but can be quite toxic in the short run. One that works great is diquat dibromide. Don't get none on you, but it is all gone shortly after application with little or no residues.

If the pond is truly not so large, well, you jest cain't beat a rake. Rake it out.

Looks like I'll be raking when water warms up. Pond is roughly 50'x160''... and fairly shallow...

I never knew that keeping a healthy pond was like taking care of a pool.
That was some good info. Thanks.