Though the mineral malachite does contain copper, the "malachite" in the dye named "malachite green" misleadingly refers to the similar color only; in fact, malachite green contains no copper at all. Kordon claims their malachite green bound in a chloride salt is less toxic to fish than oxalate versions. Don't worry over "zinc-free" malachite green: zinc would only be added to malachite green as a mordant if it were being supplied as a fabric dye.

Malachite green is quite toxic at the inflated levels recommended by its distributors, especially to fry and to adult tetras, loaches and catfish. Treated fish clear the drug rather slowly; it remains in their livers. That's why a second dosing can be more toxic than the first one. It's also quite toxic to you: a carcinogen. So scrub your fingers before you put them in your mouth, because if you get liver cancer from malachite green and die an agonizing death and they take it off the market, we'll all be so cross... Soft acidic water renders formalin/malachite green medications more effective, that is, more toxic to parasitic invertebrates but also more toxic to fishes. Use extra caution where pH is below 7.0; be prepared to do an emergency 50% water change at the first hint of distress.

In hard water malachite green may go colorless, leading you to think it isn't effective. Malachite green also increases in toxicity at higher temperatures, according to Kordon.

I think fishkeepers too casually ignore these variables.

An antidote: AmQuel will quickly bind and detoxify malachite green, as well as methylene blue and potassium permanganate.

Recommended dosage on preparations containing malachite green should be reduced to half-strength, especially where pH is lower than 7.0, even in cases where the fish you're treating aren't generally considered "sensitive." Make a careful estimate of the real net volume of water you're treating, with generous allowances for gravel and decorations. And remember that pH, temperature and dissolved organics all affect the toxicity and effectiveness of malachite green preparations: it is more toxic at lower pH, higher temperature and lower dissolved organics. So, take your own factors into account: Dave Stall, for one, found that half-dosage wasn't effective at pH 8.4:

"I can only spreak from my limited experience here, but my opinion is that malachite green/formalin at half strength is not strong enough. I don't know enough about how these meds are affected by environmental factors such as pH, temperature, and the presence of organic material to guess what strength is needed in every case. In my case, my ich outbreak simply would not respond to a half dosage of either Quick Cure or RidIch+ (both use basically the same ingredients--— malachite green and formalin). Only by increasing to full dosage was I able to contain the parasite (and that was after three weeks of daily half dosages). After increasing to full dosage, my ich was gone in a week or less, and my tetras did just fine with it. Now, there could be factors in my system that make the meds less effective. My water parameters are surely less than ideal (pH=8.4, GH=1, KH=3) and my tank is heavily planted. I don't know if this affects the meds or not, but I guess my opinion is that if medicating is the route that one decides to take, you might as well use the full dosage."

When you are protecting unhatched eggs, malachite green is dis-recommended. Eggs can turn white and fail to hatch: "Calcification" is the verdict at Fishy Farmacy, who recommend methylene blue or acriflavine instead.

Malachite green having developed some negative pres--— largely through over-dosing at toxic levels, I feel--— it has been re-labeled as "benzaldehyde green" in some formulas, or disguised as "Victoria green." The obvious solution, to reduce the dosage as recommended on the packaging, would have a dampening effect on sales, I suppose. Same stuff, nevertheless, according to a post of Ross Drewe, archived at theKrib.com. Though a May 2001 Aquarium Pharmaceuticals e-mail in response to an aquarist, subsequently posted at AquariaCentral, stated, "Malachite green and benzaldehyde green are completely different treatments," the official website for the U.S. Dept. of Health and Human Services, National Toxicology Program lists "benzaldehyde green" as an official synonym for malachite green/malachite green chloride. The link also gives the mile-long chemical name for this anti-fungal, anti-helminthic dye.

Formalin is a 37% solution of formaldehyde in distilled water, with some methanol as stabilizer. Formaldehyde (HCHO) is a powerfully toxic, carcinogenic organic compound that reacts with proteins, making it useful in tanning leather as well as an effective disinfectant. Formaldehyde reacts with dissolved oxygen and in effect removes it from the water, so you would be wise to pump in some extra air or lower the water level to get some splash from the filter. Formaldehyde also reacts with ammonia, yielding comparatively inert compounds; thus free ammonia in the water renders formaldehyde less effective. In the same vein, you'll sometimes hear that high organic content of the water, including tannins, "degrades" formalin. Conversely, formaldehyde can be used to bind and detoxify ammonia. Tropical Sciences, Inc. mutters darkly in magazine ads that other companies use formalin in their water conditioners "to break the Chloramine bond." If my sources are right, the action of formalin would more likely be to bind and detoxify the released ammonia. once the chloramine bond had been broken. Frankly, I see no dire harm in that. It's the left-over, "free" formalin that would remain toxic, if you overdosed such a conditioner, with an active half-life in water of about half a day.

Toxic paraformaldehyde. Like malachite green, formalin has also recently developed an exaggerated reputation for toxicity. When formalin is stored for long periods at the back of your fish cupboard, especially in cold, it can throw off a cloudy white precipitate--— of paraformaldehyde, which is very toxic to fishes, much more so than formalin, according to FishDoc. Formalin is oxidized by exposure to air and degraded by sunlight. Discard old formalin medications if you have doubts. FishDoc is a site you should bookmark; his brief article on malachite green/formalin is outstanding.