Countries such as AU all have work arounds, you just need to know a Vet.
As far as the stability of metro in an aquarium setting, I have yet to see any type of data to support it remaining stable for more than a 24 hr period. (best case scenario)
Of course the stability will be highly dependant on the water temp, number of fish, the organic load, lighting, etc. For most hobbyists treatment certainly should be repeated daily.
I didn't want Jay being under some kind of misguided notion that metro remains active for 7 days as his LFS had suggested, because according to all of the available data, it won't be. Not in a human (which is what this drug was designed for) and not in an aquarium setting.
And while I agree that dosing the food itself is always best, equally important is knowing how much to dose with when adding metro to food. According to Edward Noga et al & the data available in treating fish, that rate should be a min of .25% at a rate of 1% body weight per day (for 5-10 days) up to a maximum of 1% metro at a rate of 1% body weight per day, for a maximum of 3 days.
Studies have shown that when treating fish, prolonged use, or excessive use of metronidazole can lead to severe liver damage.
Even Seachem gives a very generalized dosage rate on their label for feed applications (100 mg per tablespoon of frozen food paste) with no mention of how much to feed based on the fishes body weight. I understand their reasoning as most hobbyists aren't going to weigh their sick fish, or do the math to calculate how much meds to use based on that weight. I'm just sayin .....
The beauty of magnesium sulphate is that when used to treat certain internal flagellates it has been shown to be just as effective as metro and has none of the drawbacks associated with most medications. (such as potential organ damage)
Excess magnesium sulphate simply gets flushed from the fishes system, the only real downside is that to be effective it must be fed to the fish. (in a stock solution of 3%)
HTH
!! yep i gave him a few pellets with epsom, and he did eat em...a little slow, but within 4-5 minutes all 8 pellets gone...dropped in 1 by 1...and he had to go after a few since my water pump pushed em down the tank xD hes swimming around now, re-arranging the new gravel i put in with his mouth 
