Debbie,
Here's some help with using Flubenvet 2.5% Premix.
HOW IS THE DOSE CALCULATED?
Remember 2 facts - the chx must be medicated for 7 days continuously, and using the 2.5% Premix the feed medication rate is 1.2 grams per kg of FEED.
So first you need to calculate how much feed you will need for all the birds for 7 days. If you know your birds consumption use that, but if not work on 900grams per week, per L/F bird. So for example for 20 birds that would be 20 X 0.9 = 18Kgs
HOW TO MIX
Using a large container (a trug is ideal) and rubber gloves work with a 4.5kg batch of feed at a time sprinkle some corn oil (or olive, or sunflower etc which ever is to hand or cheapest) onto the pellets and mix well so that the pellets are just slightly darkened but not softened so they disintegrate. The oil prevents the powder settling. Using a level measuring spoon sprinkle 5ml of Flubenvet powder over the surface of the 4.5kg of pellets in several passes, as evenly as you can, and mix really well as you sprinkle each pass. Continue mixing in 4.5Kg batches until the full seven days worth has been medicated. (For amounts less than 4.5kg use the Flubenvet at a rate of 1ml per 0.9Kg). Store in the medicated feed in a dry bin until you need it.
If you feed mash you can mix in the same way but don't use the oil. Use the mixture in 4 batches topping up the feeder every couple of days remixing before each time you top up so the powder doesn't settle out.
You will now have 7days worth of medicated feed you can fill their feeders from and feed for the week.
HOW TO AVOID BEING CONFUSED
Don't try to follow the rather convoluted instructions provided by Janssen and don't think about how much medication each bird needs per day. They will eat the requisit amount of wormer for their weight provided you don't feed them anything other than the medicated feed. So NO treats or unmedicated feed. If they free range it's best to confine them so they don't eat too much unmedicated food. Don't worry about overdosing, Flubenvet has been tested at up to 2.5 times the recommended dosage with no ill effects. I prefer to slightly (<20%) overdose than under which allows for any grazing they do.
WHAT IF THERE'S SOME LEFTOVER AFTER 7 DAYS?
You can either discard it or continue to feed up to nine days and then discard any but don't add unmedicated feed on top of medicated in case you expose worms to a non lethal dose which might breed resistance to the wormer.
WHAT IF I HAVE THE 1% PREMIX?
If you use the 1% Premix when mixing work in batches of 4Kg and use two scoops of the the 3gram measure provided. Make up the feed to the nearest 2kg for ease of using the measure you can always discard some.
HOW TO GET THE RIGHT MIX CONCENTRATION AND WEIGH OUT THE FEED?
You will find it is easier to work with fixed volumes of the wormer and adjust the feed weight in each batch you mix as I've done above. Weigh out a convenient weight of feed for the quantity you eventually want in a cup type scoop and mark the level with a perminent marker. There after use the scoop filled to the mark to weigh out your batches
Hope this is helpful. There's also a sticky on this topic you can look at.