Darwin Australia here.
With a 6x2x2 it would have cost way too much to pay the $11-13/150mg over the counter and a doc wont give you a script for the 20 pack of 200mg pills ($30) unless you have "serious reoccurring thrush" haha but if you know of a dodgy one they might give you a script without looking.
However the research and FAQ put together by NCRG was enough to convince a vet to give me the 4000mg I needed - costs $80 for the pills + a vet consult fee though but still cheaper than over the counter.
On day 5 of treatment and I have 2 maxima clams, 2 CBS and a long spined urchin. No ill effects seen on any of them so far (urchin hasn't been seen in 2-3 of days but regally disappears for days at a time as its small).
Not really any change yet to my Derbesia though. Some of it MIGHT be turning a bit white but I don't know if that's just because I want it to look white already or not
No increase to NO3 (still undetectable with salifert low range) and minor increase to PO4 (from 0-0.02ppm with salifert high sensitivity) but that could be from taking GFO offline.