I'm sorry, Lynn.  I'll need much more information to provide you with any kind of meaningful reply.  Copper, when applied as a pesticide within what's permitted by product labels, is effective only a subset of organisms.  Copper alone isn't likely to provide a substantial kill of most vascular plant species, but is sometimes blended with herbicides to enhance their effectiveness.  Grass Carp (sold as white amur) are selective in their feeding preferences; they won't be very effective on the plants low on their preference list, at least not initially.

Pond water levels typically fall spanning the heat of summer as evaporation outpaces precipitation.  Could that be the case here?

Do you have any sense of what plant species is/are a concern to you here?  At what size did you stock Grass Carp/white amur?  Are Largemouth Bass present?  Etc.?
Good luck with all.

Eugene

Hello,

Wanting to chime in on the question my mother asked. The pond belongs to me. I think the vegetation is just algae. I few treatments of copper sulfate very much improved it. 2 months after my last treatment of copper sulfate we purchased 7 small white amur in hopes I would not have to treat it anymore. It's been over a month and there is difference, actually getting worse.

We do have a fully stocked pond and there are some large mouth bass. I have not lived at the property to know the sizes or full range of species. I'm honestly pretty green when it comes to caring for a pond and what I should/should not be doing.

My biggest concern is should I assume the amur died and move forward with treatment of copper sulfate? Or is there someone (or recommended company) that can guide me on what I should be doing?

Thanks.

Brian

Ah . . .

This is an issue regarding white amur/Grass Carp.  They don't like to eat filamentous algae.  Their preference is for submerged species of soft-stemmed vascular plants.  Like algae, vascular plants need nutrients, space, and light.  Because white amur are selectively feeding on any vascular plants present, they're actually removing beneficial competition against filamentous algae.  Thus, at least in the short term, white amur can make algae problems worse.  They will get around to eating and potentially controlling algae, but not until they've mostly exhausted the supply of stuff that they like to eat.

Personally, I don't recommend Grass Carp/white amur as a preventative measure nor as algae control.  I only recommend them as a response to weedy coverage by a plant within their diet preferences and then only if you take the time to undrstand their limitations and tradeoffs.

Yes, formulas of copper are the standard algaecides.  However, some fishes are susceptible to copper stress, especially the minnow relatives like Grass Carp/white amur.  Be mindful that high doses of copper may even kill some.  Also, know something about your pond's water chemistry.  Hard water reacts with copper, removing its availability to act as an algaecide.  You'll need to consider higher label-recommended doses to be effective in increasingly hard water.

If you'd like to experiment with other biological control of algae, blue tilapia is a tropical fish that is finding more frequent use in Ohio because it actually likes to eat algae.  Assuming Largemouth Bass are present, I ordinarily recommend stocking relatively large fish—perhaps 7"–10" (to reduce the risk of predation)—at a density of 10–100 lbs per acre depending on the site's problematic coverage by algae.

Most to all your blue tilapia will die into an Ohio winter.  You thus get the greatest benefit from a tilapia program by stocking them in the late spring as the temperature becomes amenable.  They'll eat algae, grow—they're very prolific and may even spawn, the resultant fry providing a bit of extra forage for your bass.  Then, in the fall as the temperature drops, their metabolism slows, and they become lethargic, commit to harvesting as many as possible, perhaps even with landing nets.  Tilapia meat is a bland white protein that tastes like the butter you simmer it in . . . which is how American's seem to like to eat fish.  Thus, assuming you collect them while still alive, have at it and enjoy.  You can, of course, allow them to die over the winter; however, as dead fish decompose and release the excessive nutrients that first grew algae and then them as fish, you're right back where you started next season.

Also, keep in mind that you'd be stocking tilapia into an increasingly complex fishery/fish assemblage.  Your white amur are likely still present and eating plants.  Attacking green things from multiple angles has potential to substantially reduce their relative biomass, which could contribute to other issues like increasingly cloudy water, greater potential for blue-green algae blooms, etc.

I do hope something in this reply is of some use.

Eugene

Thank you very much for the detailed response! Will tilapia or grass carp eat watermilfoil? A google image search shows this is what is growing on the surface. 

Seems like the middle of the pond is clearing up faster than the edges, so does appear the grass carp are working, just slowly. Hoping they will move out to the edges sooner or later.

We have that and a lot of cat tail growing. I don't mind the cat tail. Just getting a little thick. So when I try to trim it down a bit the edges are super mushy. Any way to prevent that from happening?

Thanks,

Indeed, this photo shows a combination of Eurasian watermilfoil (an aggressive invasive plant) and filamentous green algae, neither of which are things that grass carp like to eat.  Tilapia will eat the algae, but watermilfoil stems are relatively coarse and not favored by herbivores in general.

If you want to hit it with an herbicide, among submerged plants, ProcellaCOR is highly selective for watermilfoils but is also a new patent tightly reined by it's manufacturer.  You'll need to consult with one of their vendors to even find out what an application will cost.  Less selective but still likely effective herbicides are diquat, endothall, 2,4-D, carfentrazone, penoxsulam, and triclopyr.  Diquat and endothall may be least restrictive for water use to follow from among these.  Endothall is formulated both as monoamine salt of endothall (which is very stressful to fish) and as dipotassium salt of endothall (which is more benign to fish).  In all cases, if you do apply a pesticide, read and strive to understand the label.

Cattail can be killed with aquatic-labeled formulas of glyphosate.  Most effective applications will be combined with a surfactant (check product labels for recommendations) and come after most of the inflorescences (the flower spikes) have matured, but before they've seeded (likely about now).

Luck,
Eugene