Copper and its effects on the koi pond
There are more organisms prematurely bumped off by well-meaning koi keepers than you would believe; far more than if nothing was added to their water. Dear Reader, and water garden enthusiast, don't let this happen to you. There are few chemical treatments that have a wide range of safety and effectiveness; one notable exception are products made of the element copper.
Copper in various formulations is useful in continuous, low doses as an algicide and epizoitic (parasiticide). Used properly it is safe and effective; copper is the only EPA approved algicide for use in potable waters. It is also one of the most common active ingredients in the field of therapeutics in aquaristics.
Two Difficulties To Consider in Using Copper:
Though it does not mal-effect true plants, some fishes, like koi and trout are sensitive to low levels of copper; most invertebrates can tolerate extremely little.
Free copper-ion availability must be present within a narrow range (0.03 to 1.0ppm, depending on species, concentration present, physical and chemical make-up of the water and system) to be effective and safe.
Leaving solution by settling out can be a problem, especially in hard, alkaline waters. Towards the ends of reducing these difficulties, copper compounds are sequestered and chelated in a few formulations; ethanol-amine complexes (e.g. cutrine), citric acid, as well as "raw" copper sulfate pentahydrate solid and solutions.
Bonding copper treatment extends inter-treatment intervals by supplying a physiological dose of copper ion over a longer period of time, much the same as the use of stabilizing conditioner with chlorine sanitizer.
Toxicity and Use:
The normal, target concentration of copper in biological systems is @ 0.3ppm free copper to a low range of 0.1 ppm free copper. The word "free" is emphasized as some assays for copper measure bound copper that is not available as biocide. An artificial, high reading may be measured using these test kits, therefore know which type of test kit and copper you are measuring.
For non-biological systems a continuous reading of 1.0 ppm is enough to assure effective algae control; more is superfluous and may damage finishes and equipment.
At pH's below 7.0, the toxicity of copper is greatly enhanced. For this reason, among others, frequent partial water changes, dilution of organics, checking and adjusting pH prior to copper treatment, if necessary, is warranted. Regular, routine maintenance and checking of water chemistry assures that the proper amount of free copper is present, without premature absorption or precipitation.
The effectiveness of copper decreases as water hardness increases. A significant reduction occurs when the bicarbonate alkalinity exceeds 150 ppm as calcium carbonate. Conversely, toxicity to fish decreases as alkalinity increases. I mention this phenomenon not so much that you should try to manipulate hardness, but that you be aware of it's effects with copper.
One of the earliest effects of having administered too much copper is apparent fish hypoxia, the loss of ability to use oxygen. Common symptoms of initial acute toxicity are fish gasping, disoriented (ataxic) at the surface, due to copper's hemolytic (blood cell splitting) and mucus-producing effects. Copper is a proteinaceous precipitant; that is, it causes your fish to produce more mucus. This may aid the in the suffocation or sloughing off of parasites, but also interferes with respiration through their skin and gills. The edge: use copper only where adequate aeration, crowding is not problematical.
Temperature and Light; Timing Copper Administration:
Copper is almost ineffective at temperatures below 60 degrees F. and likewise more algicidal when algae are at their most active metabolically. Sunny days between 10:00 and 2:00 are optimal treatment times. Overcast or murky waters are contraindicated; wait till it's warm and sunny to apply copper.
Toxicity to Livestock:
Koi carp begin show signs of copper-effect at @ 0.03 ppm and may be killed under various circumstances as elucidated above, at near the target concentration.
Other species of "native" fishes; trout, sunfishes, catfish are even more sensitive, dying near concentrations near 0.10 ppm. Most desirable aquatic plants are unaffected at these doses. Note label precautions on application & rates due to different species' sensitivities.
For large, lake-size systems copper sulfate, with or without additives, crystals or granular may be spread by hand or equipment. Large crystals can be burlap-bagged and towed behind a boat.
For smaller water gardens solutions may be distributed as copper-alkano-amine complexes (e.g. Cutrine) and other chelated formulations below or above water by sprayer or watering can. Use system water as a carrier. These compounds are safer to use with fish than "raw" copper sulfate.
For aerial distribution, I'd wear goggles to avoid contact with eyes, and flush with water if skin contact occurs. It is suggested that you wear gloves and avoid breathing copper dust. There is a very low toxicity to humans; there may be 1.0 ppm or more free copper in your drinking water.
Copper is very corrosive to metals; rinse equipment three times with fresh water and other materials that come in contact (e.g. truck beds).
Storage of Copper Treatments:
Dry compounds are hygroscopic; they get "lumpy" if exposed to the air. Keep dried copper compounds in rolled bags, out of moistures way, stored in a locker. Copper Sulfate (CuSO4) is also considered a strong oxidizer; dry products must be stored away from solvents and other petroleum products.
Chronic to Acute Toxicity:
Precipitated copper may come back dangerously into solution in toxic concentration with a change in chemical and physical conditions. Toxicity can be important in situations where the bottom detritus is stirred up, pH lowered, water softened, oxygen concentration lowered, and/or temperature elevated. In particular a sudden to chronic lowering of pH coupled with water softening and/or raising of temperature may cause re-release of "lost", bound copper, with disastrous results. The edge: once again, frequent, partial, continuous water quality maintenance (you) will preclude this disaster.
Steps to Using Copper:
1) Measure, know the total gallonage of system, species make-up, treatment mode, concentration for system.
2) Check and note the systems pH, temperature, existing copper concentration and possibly oxygen levels.
3) Vent, vacuum otherwise treat the system to remove organics, adjust water quality.
4) Treat system as outlined. For example, with no readable copper level 1 oz. or 20 mls. of cutrine per 2000 gallons will produce 0.30 ppm free copper initially. This is at the high end for biological systems.
Due to the efficacy of use; measure and treat frequently at lower concentrations to provide enough free copper continuously. If a system "gets away from you" and generates an algal bloom it may be necessary to dump it initially or treat in another way at first.
Copper compounds in various applications do have their place as algicides, parasite controls and anti-fouling agents. Their use is not without difficulties however. Consideration must be made for the chemical, physical and biological make-up of the intended treatment system. Though safety margins are sometimes small, copper is and appears will continue to be a relatively safe and useful element in biological systems. Use it knowledgeably and with frequent testing.