Could you get away with a slightly heaped 1/4 teaspoon with 625 milligrams or .625 of a gram of the Levamisole?

He also notes elsewhere that because anthelmintics don't dissolve real well, overdosing isn't very easy to do. So a little imprecision may be ok. (Maggie's fudge factor on commercial applications comes to mind too).

That casual comment about not being able to over dose, is a little inconsistent with the advice to do a 100% water change with seasoned water, so a residual doesn't build up. But I think absolute measurement isn't needed here, so long as we aren't letting the stuff accumulate through only partial water changes.

I have cautioned against 100% water changes usually, but IF this is an established tank and IF the gravel, filter media (just the biological media) and plants (?) have been there a few months and are not allowed to dry out, there shouldn't be a huge ammonia surge. Since the fish are being medicated, feeding is going to be more careful and modest anyway.

By the way, Charles also suggested "for a measure of economy", only putting half the water in a 10-gallon tank, so one didn't have to use as much of the treatment. (My response, of course, was Doh!) If there is an airstone or hard airline run in there to mix things up, it should be ok, assuming the room temperature is appropriate.

If available changing water is limited, that is another reason to scale down tank contents.