Now it's been pointed out to me by ANHBUC there's two threads on this currently running which is very confusing the below maybe a little on the late side. Please can people just use one thread in future.
Re the correct dosage of F'vet for gapeworm I'm not aware of the advice to dble the dose but I did wonder if it might be needed. In fact F'vet is very safe and you can overdose without ill effects so increasing the dose to dble I believe wouldn't cause a problem. My understanding is that it has been tested to 2.5 times dosage with no ill effects and in fact I usually err on the side of overdosing to allow for a little grazing feeding.
I'd be a little concerned with chx about though. Maybe try the grape dasing trick and feed to mum only which isn't a very accurate way in any case. The following should work.
A health hen of L/F size should eat around 800grms to 1 kg per week so working on 1kg and 1% F'vet she will need 3grams. Measure out a half teaspoonful of F (2.5ml measure) and place on a clean flat surface. Make a line of it roughly of even density and divide it up with a knife into 8 piles by halfing each pile repeatedly. each day put one pile into a grape and hand feed. Give her 2 grapes the first day. If you want to dble dose use the supplied scoop which gives 6 grammes to start with.
PS be sure and do this where your actions won't be misinterpreted ie definitely not when out clubbing or at a Rave or you might find yourself the guest of the local police.
HF