This is the reply I got from the company:
Thank you very much for contacting us regarding our products. All of your comments and questions are valuable. We use your feedback to create the most effective line of aquarium and pond products available.
Sara as you surmised, this is simply a story that somehow “got legs,” with no real basis in fact. Melafix was, and is tested with labyrinth fish on a frequent basis, not only on the common species in the trade, but also less common varieties like chocolate gouramies and various wild bettas. I’ll ignore the thousands of consumers who use it successfully with labyrinth fishes of all kinds every year. Actually, I won’t completely: One of the most popular betta remedies out there, Bettafix, IS Melafix, merely in a more dilute form to make dosing simpler for smaller aquariums (though the final therapeutic concentration is the same as for Melafix).
I suspect the story developed when one hobbyist jumped to a conclusion after losing fish following treatment with Melafix (the fish was likely too far gone, or, as often happens, the fish had some illness that Melafix will not treat, like ich), and posted his or her experience online. Someone else saw that post, and “confirmation bias” took its inexorable course. But we can assure you, and any other hobbyists out there, that Melafix is quite safe for any labyrinth fish, be they bettas, gouramies, climbing perches, bushfish, or anything else.
If you have any other questions or wish to discuss this further, please email back or give us a call at 1-800-847-0659.
Technical Service and Research