Copper has been use in aquaculture for decades. Like aspirin for humans has been buffered, so copper has evolved into other forms to improve its stability, effectiveness to target the microbe, and leave the fish healthy.
Copper additions in the early years was precipitated out from salt water by carbonates that make up the alkalinity. The aquaculture industry needed a more stable copper that would stay in soluble form and thus keep a more or less constant concentration. The industry didn't want to do copper measurements and additions every few hours.
This was just the beginning. Along came home aquarists with tank decorations and other contents. These coppers were also removed from the water by carbonate substrates, rocks and other calcareous deposits. In the home aquarium, such coppers were held in even less constant concentrations. Not only were they coming out of solution, but a certain quantity comes out of solution at a specific pH such that, as the pH goes down, less is precipitated. As a converse, as the pH goes down, the copper that was precipitated at the higher pH would re-disslove. This, you can imagine could release a lot copper and raise its level much too high for the fishes.
Copper treatments
had and have to be done in a quarantine tank. Because no matter how much we have stabilized the copper, the pH controls to some extent how much copper stays in solution.
The next generation of coppers evolved a kind of protected copper. The easiest was found to chelate (pronounced KEYlate) the copper. This isn't a chemical bond. This is more like a loose tie or shield by a large molecule over the relatively small copper ion.
These chelated copper medications then were widely distributed and sold as a much more stable form of administering copper. And they were. Still, though, the copper ion was free to do its job at making life miserable for the microbe. Unfortunately, it was still free to poison our fishes. The concentration of these chelated coppers had to be controlled closely since the copper ion was very much assessable to complex with hemoglobin and other fish chemistries and cause stress and even death to the fish.
Because of this, copper compounds and even chelated copper compounds were not recommended for use on what were considered fishes sensitive to copper. They included tangs and many angelfishes.
Another generation of copper meds slowly evolved to increase the stability of the copper concentration, and at the same time, not allow the copper to be as readily accessible to the fish, yet still do its thing with the microbe. These compounds of copper are not chelated. The copper is chemically bonded to another molecule that keeps the copper at arm's length from the fish and still puts it 'in the face' of the microbe. One such medication is Cupramine.
This kind of compound is much safer for marine fishes and has successfully been used on even the most sensitive of marine fishes, and even marine creatures that should not come in contact with copper at all. It needs only be used in low concentrations; has a good effective concentration range so the aquarist doesn't have to be paranoid about checking the copper hourly to keep it in the lethal-to-the-microbe range; and is effective.
That's about the best I can do without getting chemical on you!
