Is the coarse mix dusty maybe end of a bag ,does he only do it when eating ? For small amounts of wormer try your vet they may have lots of people requireing smallamounts and have open containers or try SFS its what they do, i only know of panacur in 250 mls most wormers smallest is 1lt some of the injectables are in 100 or 250 mls but its a tiny amount per sheep 1or 2 ml. YES if you worm on a regular basis you need to change types eg i do 1year white wormer 2nd year yellow wormer 3rd year clear wormer 4th year clear wormer then start again , but change type not just name of wormer. There are 3 main flukicides and they must also be changed fasinex/flukiver/trodax. TO stop resistance it is more important to dose at the correct weight.