As you have six hens, you need to weigh out 6 kilos of pellets.Put about one kilo into a second large container, and add a small amount if vegetable oil, just enough to lightly coat the pellets, so the Flubenvet powder will stick to them. Stir them well, then add the right amount of powder, which will be 3 level scoops ( using scoop provided.) Stir carefully, then gradually add the rest of the feed in batches, mixing well each time.
Empty the feeder and refill with treated pellets. Feed ONLY THESE for 7 days, no other treats (although I do give my girls some greens in the evening, once they've eaten enough pellets that day.) The idea is that, if only fed treated pellets, each hen will self-dose with the correct amount for her bodyweight. If fed other treats, she may not get an effective dose.
You can buy pre-treated pellets, but they can be wasteful as any left over will be out of date before the next worming, or else the bag will run out before the week is up. The powder can be stored for the three treatments you can get out of one pot for six hens, so if well in date when you buy it, it's the best way to buy.
This method entails confining the hens in a closed run for the week. It's definitely the best way, as the medicine goes down gradually, sort of drip-fed bit by bit. However, if they're in a run which is too small for them 24/7, you could try Method 2, based on treat feeding all in one daily dose. For this method, they are allowed to free range as normal, but have to be hungry enough to eat the treated corn enthusiastically (not difficult!)
For 6 hens, find a small mug to use as a measure. Put 7 mugfuls into a large container. Add oil and 3 scoops of Flubenvet powder mixed as before, only making up to a more concentrated feed. Put a large plate or similar off the ground on a block, and give the hens one mugful per day to share. Watch carefully, as with this method, the boss hens may get more than their share and the lower ranking ones may not get enough. If so, you may need to separate the timid ones and feed them their share separately. This method does get it into them, but has obvious disadvantages compared with just feeding treated pellets for 7 days, no fuss.
Vermex used to claim to kill worms, but this claim had to be dropped following complaints and tests, showing it didn't actually have any effect. I never use it myself, my hens seem to stay healthy and lay well on a simple diet and no supplements. But lots of people do like to feed various extras to their birds, and if your purse is deep enough, I suppose they do no harm. Flubenvet is the only effective wormer licensed for poultry, and it's safe to eat eggs produced whilst using it.
It's good to keep up to date with worming, but there may be other reasons for softies in a young hen. Sometimes, even with a vaccinated hen, there may have been a low-level infection as a grower, which can have an effect on laying performance later on. If so, nothing really that can be done about it. See Poutrykeeper https://poultrykeeper.com/egg-problems/soft-thin-or-missing-egg-shells/
