Methylene blue is a drug, the drug put too much certainly something, if you really think that put too much, while your fish poisoning is not deep when the water change, the drug dilution, add oxygen, do not wait until your fish have a reaction to take measures, then it may be too late, because people can be poisoned by gastric lavage, but the fish may not be able to, I have raised the fish poisoned with drugs twice, once I found in time to save (maple, parrot, a whole tank), and once when I found it has been hanging (pearl scales)

. I've had two fish poisoned by drugs, one I found in time and saved it (mapfish, parrot fish, a whole tank), and the other time when I found it, it had already hung up (pearl scales)