afremont the issue with that link is its not considering the actual % levamisole. That link is correct for whatever purity they are using, but they don't say what it is. It could be 90% or maybe a 70% powder. I mentioned the ebay stuff as being questionable as it does not look anything like mine. If it was very diluted then that would explain the much higher dosage. However your description of its effects are not at all like levamisole. It should not cloud or stress fish or snails at all. My fish still eat everything when I add the med my snails behave normally.
In comparison below is what I have always used. My levamisole was produced by Agrilabs and I believe they no longer make it.
The ebay seller is selling a white powder as levamisole. I suggested it may not be levamisole because it does not look like it nor does the dosage or instructions match up.
Let us know how the second trial of the ebay stuff goes. If its still a flop I might be able to send you some of what I have if you want to try it. It is expired but was still working 6 months ago. Other then that I can just suggest the bird dewormer or ask a vet. I'm pretty sure the main reason its so hard to get levamisole these days is because it is increasingly found in cocaine. I bought mine in 07' or 08' off a shelf in my local fleetfarm. Now its almost impossible to fine anywhere for a decent price. Next time I go to Mexico..... >.>